diff --git a/icu4c/source/common/cmemory.h b/icu4c/source/common/cmemory.h
index 7f7fd8d..8d60442 100644
--- a/icu4c/source/common/cmemory.h
+++ b/icu4c/source/common/cmemory.h
@@ -274,7 +274,10 @@
  *
  * WARNING: MaybeStackArray only works with primitive (plain-old data) types.
  * It does NOT know how to call a destructor! If you work with classes with
- * destructors, consider LocalArray in localpointer.h or MemoryPool.
+ * destructors, consider:
+ *
+ * - LocalArray in localpointer.h if you know the length ahead of time
+ * - MaybeStackVector if you know the length at runtime
  */
 template<typename T, int32_t stackCapacity>
 class MaybeStackArray {
@@ -684,26 +687,26 @@
 template<typename T, int32_t stackCapacity = 8>
 class MemoryPool : public UMemory {
 public:
-    MemoryPool() : count(0), pool() {}
+    MemoryPool() : fCount(0), fPool() {}
 
     ~MemoryPool() {
-        for (int32_t i = 0; i < count; ++i) {
-            delete pool[i];
+        for (int32_t i = 0; i < fCount; ++i) {
+            delete fPool[i];
         }
     }
 
     MemoryPool(const MemoryPool&) = delete;
     MemoryPool& operator=(const MemoryPool&) = delete;
 
-    MemoryPool(MemoryPool&& other) U_NOEXCEPT : count(other.count),
-                                                pool(std::move(other.pool)) {
-        other.count = 0;
+    MemoryPool(MemoryPool&& other) U_NOEXCEPT : fCount(other.fCount),
+                                                fPool(std::move(other.fPool)) {
+        other.fCount = 0;
     }
 
     MemoryPool& operator=(MemoryPool&& other) U_NOEXCEPT {
-        count = other.count;
-        pool = std::move(other.pool);
-        other.count = 0;
+        fCount = other.fCount;
+        fPool = std::move(other.fPool);
+        other.fCount = 0;
         return *this;
     }
 
@@ -716,20 +719,101 @@
      */
     template<typename... Args>
     T* create(Args&&... args) {
-        int32_t capacity = pool.getCapacity();
-        if (count == capacity &&
-            pool.resize(capacity == stackCapacity ? 4 * capacity : 2 * capacity,
-                        capacity) == nullptr) {
+        int32_t capacity = fPool.getCapacity();
+        if (fCount == capacity &&
+            fPool.resize(capacity == stackCapacity ? 4 * capacity : 2 * capacity,
+                         capacity) == nullptr) {
             return nullptr;
         }
-        return pool[count++] = new T(std::forward<Args>(args)...);
+        return fPool[fCount++] = new T(std::forward<Args>(args)...);
     }
 
-private:
-    int32_t count;
-    MaybeStackArray<T*, stackCapacity> pool;
+    /**
+     * @return Number of elements that have been allocated.
+     */
+    int32_t count() const {
+        return fCount;
+    }
+
+protected:
+    int32_t fCount;
+    MaybeStackArray<T*, stackCapacity> fPool;
 };
 
+/**
+ * An internal Vector-like implementation based on MemoryPool.
+ *
+ * Heap-allocates each element and stores pointers.
+ *
+ * To append an item to the vector, use emplaceBack.
+ *
+ *     MaybeStackVector<MyType> vector;
+ *     MyType* element = vector.emplaceBack();
+ *     if (!element) {
+ *         status = U_MEMORY_ALLOCATION_ERROR;
+ *     }
+ *     // do stuff with element
+ *
+ * To loop over the vector, use a for loop with indices:
+ *
+ *     for (int32_t i = 0; i < vector.length(); i++) {
+ *         MyType* element = vector[i];
+ *     }
+ */
+template<typename T, int32_t stackCapacity = 8>
+class MaybeStackVector : protected MemoryPool<T, stackCapacity> {
+public:
+    using MemoryPool<T, stackCapacity>::MemoryPool;
+    using MemoryPool<T, stackCapacity>::operator=;
+
+    template<typename... Args>
+    T* emplaceBack(Args&&... args) {
+        return this->create(args...);
+    }
+
+    int32_t length() const {
+        return this->fCount;
+    }
+
+    T** getAlias() {
+        return this->fPool.getAlias();
+    }
+
+    /**
+     * Array item access (read-only).
+     * No index bounds check.
+     * @param i array index
+     * @return reference to the array item
+     */
+    const T* operator[](ptrdiff_t i) const {
+        return this->fPool[i];
+    }
+
+    /**
+     * Array item access (writable).
+     * No index bounds check.
+     * @param i array index
+     * @return reference to the array item
+     */
+    T* operator[](ptrdiff_t i) {
+        return this->fPool[i];
+    }
+
+    /**
+     * Append all the items from another MaybeStackVector to this one.
+     */
+    void appendAll(const MaybeStackVector& other, UErrorCode& status) {
+        for (int32_t i = 0; i < other.fCount; i++) {
+            T* item = emplaceBack(*other[i]);
+            if (!item) {
+                status = U_MEMORY_ALLOCATION_ERROR;
+                return;
+            }
+        }
+    }
+};
+
+
 U_NAMESPACE_END
 
 #endif  /* __cplusplus */
diff --git a/icu4c/source/i18n/Makefile.in b/icu4c/source/i18n/Makefile.in
index b72f79b..ae2c71a 100644
--- a/icu4c/source/i18n/Makefile.in
+++ b/icu4c/source/i18n/Makefile.in
@@ -97,7 +97,7 @@
 ztrans.o zrule.o vzone.o fphdlimp.o fpositer.o ufieldpositer.o \
 decNumber.o decContext.o alphaindex.o tznames.o tznames_impl.o tzgnames.o \
 tzfmt.o compactdecimalformat.o gender.o region.o scriptset.o \
-uregion.o reldatefmt.o quantityformatter.o measunit.o \
+uregion.o reldatefmt.o quantityformatter.o measunit.o measunit_extra.o \
 sharedbreakiterator.o scientificnumberformatter.o dayperiodrules.o nounit.o \
 number_affixutils.o number_compact.o number_decimalquantity.o \
 number_decimfmtprops.o number_fluent.o number_formatimpl.o number_grouping.o \
diff --git a/icu4c/source/i18n/currunit.cpp b/icu4c/source/i18n/currunit.cpp
index dab6dda..280bd56 100644
--- a/icu4c/source/i18n/currunit.cpp
+++ b/icu4c/source/i18n/currunit.cpp
@@ -19,9 +19,7 @@
 #include "cstring.h"
 #include "uinvchar.h"
 #include "charstr.h"
-
-static constexpr char16_t kDefaultCurrency[] = u"XXX";
-static constexpr char kDefaultCurrency8[] = "XXX";
+#include "measunit_impl.h"
 
 U_NAMESPACE_BEGIN
 
diff --git a/icu4c/source/i18n/i18n.vcxproj b/icu4c/source/i18n/i18n.vcxproj
index 5c6760d..531a9a0 100644
--- a/icu4c/source/i18n/i18n.vcxproj
+++ b/icu4c/source/i18n/i18n.vcxproj
@@ -187,6 +187,7 @@
     <ClCompile Include="ulistformatter.cpp" />
     <ClCompile Include="measfmt.cpp" />
     <ClCompile Include="measunit.cpp" />
+    <ClCompile Include="measunit_extra.cpp" />
     <ClCompile Include="measure.cpp" />
     <ClCompile Include="msgfmt.cpp" />
     <ClCompile Include="nfrs.cpp" />
@@ -392,6 +393,7 @@
     <ClInclude Include="indiancal.h" />
     <ClInclude Include="islamcal.h" />
     <ClInclude Include="japancal.h" />
+    <ClInclude Include="measunit_impl.h" />
     <ClInclude Include="msgfmt_impl.h" />
     <ClInclude Include="nfrlist.h" />
     <ClInclude Include="nfrs.h" />
diff --git a/icu4c/source/i18n/i18n.vcxproj.filters b/icu4c/source/i18n/i18n.vcxproj.filters
index a1813fc..50a06ee 100644
--- a/icu4c/source/i18n/i18n.vcxproj.filters
+++ b/icu4c/source/i18n/i18n.vcxproj.filters
@@ -204,6 +204,9 @@
     <ClCompile Include="measunit.cpp">
       <Filter>formatting</Filter>
     </ClCompile>
+    <ClCompile Include="measunit_extra.cpp">
+      <Filter>formatting</Filter>
+    </ClCompile>
     <ClCompile Include="measure.cpp">
       <Filter>formatting</Filter>
     </ClCompile>
@@ -830,6 +833,9 @@
     <ClInclude Include="japancal.h">
       <Filter>formatting</Filter>
     </ClInclude>
+    <ClInclude Include="measunit_impl.h">
+      <Filter>formatting</Filter>
+    </ClInclude>
     <ClInclude Include="msgfmt_impl.h">
       <Filter>formatting</Filter>
     </ClInclude>
diff --git a/icu4c/source/i18n/i18n_uwp.vcxproj b/icu4c/source/i18n/i18n_uwp.vcxproj
index 989cef8..0268132 100644
--- a/icu4c/source/i18n/i18n_uwp.vcxproj
+++ b/icu4c/source/i18n/i18n_uwp.vcxproj
@@ -408,6 +408,7 @@
     <ClCompile Include="ulistformatter.cpp" />
     <ClCompile Include="measfmt.cpp" />
     <ClCompile Include="measunit.cpp" />
+    <ClCompile Include="measunit_extra.cpp" />
     <ClCompile Include="measure.cpp" />
     <ClCompile Include="msgfmt.cpp" />
     <ClCompile Include="nfrs.cpp" />
@@ -611,6 +612,7 @@
     <ClInclude Include="indiancal.h" />
     <ClInclude Include="islamcal.h" />
     <ClInclude Include="japancal.h" />
+    <ClInclude Include="measunit_impl.h" />
     <ClInclude Include="msgfmt_impl.h" />
     <ClInclude Include="nfrlist.h" />
     <ClInclude Include="nfrs.h" />
diff --git a/icu4c/source/i18n/measunit.cpp b/icu4c/source/i18n/measunit.cpp
index 5ce9f54..344ba45 100644
--- a/icu4c/source/i18n/measunit.cpp
+++ b/icu4c/source/i18n/measunit.cpp
@@ -17,9 +17,11 @@
 #if !UCONFIG_NO_FORMATTING
 
 #include "unicode/uenum.h"
+#include "unicode/errorcode.h"
 #include "ustrenum.h"
 #include "cstring.h"
 #include "uassert.h"
+#include "measunit_impl.h"
 
 U_NAMESPACE_BEGIN
 
@@ -535,7 +537,7 @@
     "solar-mass",
     "stone",
     "ton",
-    "base",
+    "one",
     "percent",
     "permille",
     "gigawatt",
@@ -2006,24 +2008,62 @@
     return -1;
 }
 
-MeasureUnit::MeasureUnit() {
-    fCurrency[0] = 0;
-    fTypeId = kBaseTypeIdx;
-    fSubTypeId = kBaseSubTypeIdx;
+MeasureUnit::MeasureUnit() : MeasureUnit(kBaseTypeIdx, kBaseSubTypeIdx) {
+}
+
+MeasureUnit::MeasureUnit(int32_t typeId, int32_t subTypeId)
+        : fImpl(nullptr), fSubTypeId(subTypeId), fTypeId(typeId) {
 }
 
 MeasureUnit::MeasureUnit(const MeasureUnit &other)
-        : fTypeId(other.fTypeId), fSubTypeId(other.fSubTypeId) {
-    uprv_strcpy(fCurrency, other.fCurrency);
+        : fImpl(nullptr) {
+    *this = other;
+}
+
+MeasureUnit::MeasureUnit(MeasureUnit &&other) noexcept
+        : fImpl(other.fImpl),
+        fSubTypeId(other.fSubTypeId),
+        fTypeId(other.fTypeId) {
+    other.fImpl = nullptr;
+}
+
+MeasureUnit::MeasureUnit(MeasureUnitImpl&& impl)
+        : fImpl(nullptr), fSubTypeId(-1), fTypeId(-1) {
+    if (!findBySubType(impl.identifier.toStringPiece(), this)) {
+        fImpl = new MeasureUnitImpl(std::move(impl));
+    }
 }
 
 MeasureUnit &MeasureUnit::operator=(const MeasureUnit &other) {
     if (this == &other) {
         return *this;
     }
+    delete fImpl;
+    if (other.fImpl) {
+        ErrorCode localStatus;
+        fImpl = new MeasureUnitImpl(other.fImpl->copy(localStatus));
+        if (!fImpl || localStatus.isFailure()) {
+            // Unrecoverable allocation error; set to the default unit
+            *this = MeasureUnit();
+            return *this;
+        }
+    } else {
+        fImpl = nullptr;
+    }
     fTypeId = other.fTypeId;
     fSubTypeId = other.fSubTypeId;
-    uprv_strcpy(fCurrency, other.fCurrency);
+    return *this;
+}
+
+MeasureUnit &MeasureUnit::operator=(MeasureUnit &&other) noexcept {
+    if (this == &other) {
+        return *this;
+    }
+    delete fImpl;
+    fImpl = other.fImpl;
+    other.fImpl = nullptr;
+    fTypeId = other.fTypeId;
+    fSubTypeId = other.fSubTypeId;
     return *this;
 }
 
@@ -2032,14 +2072,28 @@
 }
 
 MeasureUnit::~MeasureUnit() {
+    delete fImpl;
+    fImpl = nullptr;
 }
 
 const char *MeasureUnit::getType() const {
+    // We have a type & subtype only if fTypeId is present.
+    if (fTypeId == -1) {
+        return "";
+    }
     return gTypes[fTypeId];
 }
 
 const char *MeasureUnit::getSubtype() const {
-    return fCurrency[0] == 0 ? gSubTypes[getOffset()] : fCurrency;
+    // We have a type & subtype only if fTypeId is present.
+    if (fTypeId == -1) {
+        return "";
+    }
+    return getIdentifier();
+}
+
+const char *MeasureUnit::getIdentifier() const {
+    return fImpl ? fImpl->identifier.data() : gSubTypes[getOffset()];
 }
 
 UBool MeasureUnit::operator==(const UObject& other) const {
@@ -2050,10 +2104,7 @@
         return FALSE;
     }
     const MeasureUnit &rhs = static_cast<const MeasureUnit&>(other);
-    return (
-            fTypeId == rhs.fTypeId
-            && fSubTypeId == rhs.fSubTypeId
-            && uprv_strcmp(fCurrency, rhs.fCurrency) == 0);
+    return uprv_strcmp(getIdentifier(), rhs.getIdentifier()) == 0;
 }
 
 int32_t MeasureUnit::getIndex() const {
@@ -2153,42 +2204,14 @@
     return false;
 }
 
-bool MeasureUnit::parseCoreUnitIdentifier(
-        StringPiece coreUnitIdentifier,
-        MeasureUnit* numerator,
-        MeasureUnit* denominator,
-        UErrorCode& status) {
-    if (U_FAILURE(status)) {
-        return false;
-    }
-
-    // First search for the whole code unit identifier as a subType
-    if (findBySubType(coreUnitIdentifier, numerator)) {
-        return false; // found a numerator but not denominator
-    }
-
-    // If not found, try breaking apart numerator and denominator
-    int32_t perIdx = coreUnitIdentifier.find("-per-", 0);
-    if (perIdx == -1) {
-        // String does not contain "-per-"
-        status = U_ILLEGAL_ARGUMENT_ERROR;
-        return false;
-    }
-    StringPiece numeratorStr(coreUnitIdentifier, 0, perIdx);
-    StringPiece denominatorStr(coreUnitIdentifier, perIdx + 5);
-    if (findBySubType(numeratorStr, numerator) && findBySubType(denominatorStr, denominator)) {
-        return true; // found both a numerator and denominator
-    }
-
-    // The numerator or denominator were invalid
-    status = U_ILLEGAL_ARGUMENT_ERROR;
-    return false;
-}
-
 MeasureUnit MeasureUnit::resolveUnitPerUnit(
         const MeasureUnit &unit, const MeasureUnit &perUnit, bool* isResolved) {
     int32_t unitOffset = unit.getOffset();
     int32_t perUnitOffset = perUnit.getOffset();
+    if (unitOffset == -1 || perUnitOffset == -1) {
+        *isResolved = false;
+        return MeasureUnit();
+    }
 
     // binary search for (unitOffset, perUnitOffset)
     int32_t start = 0;
@@ -2236,18 +2259,24 @@
     fSubTypeId = result - gOffsets[fTypeId]; 
 }
 
-void MeasureUnit::initCurrency(const char *isoCurrency) {
+void MeasureUnit::initCurrency(StringPiece isoCurrency) {
     int32_t result = binarySearch(gTypes, 0, UPRV_LENGTHOF(gTypes), "currency");
     U_ASSERT(result != -1);
     fTypeId = result;
     result = binarySearch(
             gSubTypes, gOffsets[fTypeId], gOffsets[fTypeId + 1], isoCurrency);
-    if (result != -1) {
-        fSubTypeId = result - gOffsets[fTypeId];
-    } else {
-        uprv_strncpy(fCurrency, isoCurrency, UPRV_LENGTHOF(fCurrency));
-        fCurrency[3] = 0;
+    if (result == -1) {
+        fImpl = new MeasureUnitImpl(MeasureUnitImpl::forCurrencyCode(isoCurrency));
+        if (fImpl) {
+            fSubTypeId = -1;
+            return;
+        }
+        // malloc error: fall back to the undefined currency
+        result = binarySearch(
+            gSubTypes, gOffsets[fTypeId], gOffsets[fTypeId + 1], kDefaultCurrency8);
+        U_ASSERT(result != -1);
     }
+    fSubTypeId = result - gOffsets[fTypeId];
 }
 
 void MeasureUnit::initNoUnit(const char *subtype) {
@@ -2262,10 +2291,14 @@
 void MeasureUnit::setTo(int32_t typeId, int32_t subTypeId) {
     fTypeId = typeId;
     fSubTypeId = subTypeId;
-    fCurrency[0] = 0;
+    delete fImpl;
+    fImpl = nullptr;
 }
 
 int32_t MeasureUnit::getOffset() const {
+    if (fTypeId < 0 || fSubTypeId < 0) {
+        return -1;
+    }
     return gOffsets[fTypeId] + fSubTypeId;
 }
 
diff --git a/icu4c/source/i18n/measunit_extra.cpp b/icu4c/source/i18n/measunit_extra.cpp
new file mode 100644
index 0000000..d848965
--- /dev/null
+++ b/icu4c/source/i18n/measunit_extra.cpp
@@ -0,0 +1,783 @@
+// © 2020 and later: Unicode, Inc. and others.
+// License & terms of use: http://www.unicode.org/copyright.html
+
+// Extra functions for MeasureUnit not needed for all clients.
+// Separate .o file so that it can be removed for modularity.
+
+#include "unicode/utypes.h"
+
+#if !UCONFIG_NO_FORMATTING
+
+// Allow implicit conversion from char16_t* to UnicodeString for this file:
+// Helpful in toString methods and elsewhere.
+#define UNISTR_FROM_STRING_EXPLICIT
+
+#include "cstring.h"
+#include "measunit_impl.h"
+#include "uarrsort.h"
+#include "uassert.h"
+#include "ucln_in.h"
+#include "umutex.h"
+#include "unicode/errorcode.h"
+#include "unicode/localpointer.h"
+#include "unicode/measunit.h"
+#include "unicode/ucharstrie.h"
+#include "unicode/ucharstriebuilder.h"
+
+#include "cstr.h"
+
+U_NAMESPACE_BEGIN
+
+
+namespace {
+
+// TODO: Propose a new error code for this?
+constexpr UErrorCode kUnitIdentifierSyntaxError = U_ILLEGAL_ARGUMENT_ERROR;
+
+// This is to ensure we only insert positive integers into the trie
+constexpr int32_t kSIPrefixOffset = 64;
+
+constexpr int32_t kCompoundPartOffset = 128;
+
+enum CompoundPart {
+    COMPOUND_PART_PER = kCompoundPartOffset,
+    COMPOUND_PART_TIMES,
+    COMPOUND_PART_PLUS,
+};
+
+constexpr int32_t kPowerPartOffset = 256;
+
+enum PowerPart {
+    POWER_PART_P2 = kPowerPartOffset + 2,
+    POWER_PART_P3,
+    POWER_PART_P4,
+    POWER_PART_P5,
+    POWER_PART_P6,
+    POWER_PART_P7,
+    POWER_PART_P8,
+    POWER_PART_P9,
+    POWER_PART_P10,
+    POWER_PART_P11,
+    POWER_PART_P12,
+    POWER_PART_P13,
+    POWER_PART_P14,
+    POWER_PART_P15,
+};
+
+constexpr int32_t kSimpleUnitOffset = 512;
+
+const struct SIPrefixStrings {
+    const char* const string;
+    UMeasureSIPrefix value;
+} gSIPrefixStrings[] = {
+    { "yotta", UMEASURE_SI_PREFIX_YOTTA },
+    { "zetta", UMEASURE_SI_PREFIX_ZETTA },
+    { "exa", UMEASURE_SI_PREFIX_EXA },
+    { "peta", UMEASURE_SI_PREFIX_PETA },
+    { "tera", UMEASURE_SI_PREFIX_TERA },
+    { "giga", UMEASURE_SI_PREFIX_GIGA },
+    { "mega", UMEASURE_SI_PREFIX_MEGA },
+    { "kilo", UMEASURE_SI_PREFIX_KILO },
+    { "hecto", UMEASURE_SI_PREFIX_HECTO },
+    { "deka", UMEASURE_SI_PREFIX_DEKA },
+    { "deci", UMEASURE_SI_PREFIX_DECI },
+    { "centi", UMEASURE_SI_PREFIX_CENTI },
+    { "milli", UMEASURE_SI_PREFIX_MILLI },
+    { "micro", UMEASURE_SI_PREFIX_MICRO },
+    { "nano", UMEASURE_SI_PREFIX_NANO },
+    { "pico", UMEASURE_SI_PREFIX_PICO },
+    { "femto", UMEASURE_SI_PREFIX_FEMTO },
+    { "atto", UMEASURE_SI_PREFIX_ATTO },
+    { "zepto", UMEASURE_SI_PREFIX_ZEPTO },
+    { "yocto", UMEASURE_SI_PREFIX_YOCTO },
+};
+
+// TODO(ICU-20920): Get this list from data
+const char16_t* const gSimpleUnits[] = {
+    u"one", // note: expected to be index 0
+    u"candela",
+    u"carat",
+    u"gram",
+    u"ounce",
+    u"ounce-troy",
+    u"pound",
+    u"kilogram",
+    u"stone",
+    u"ton",
+    u"metric-ton",
+    u"earth-mass",
+    u"solar-mass",
+    u"point",
+    u"inch",
+    u"foot",
+    u"yard",
+    u"meter",
+    u"fathom",
+    u"furlong",
+    u"mile",
+    u"nautical-mile",
+    u"mile-scandinavian",
+    u"100-kilometer",
+    u"earth-radius",
+    u"solar-radius",
+    u"astronomical-unit",
+    u"light-year",
+    u"parsec",
+    u"second",
+    u"minute",
+    u"hour",
+    u"day",
+    u"day-person",
+    u"week",
+    u"week-person",
+    u"month",
+    u"month-person",
+    u"year",
+    u"year-person",
+    u"decade",
+    u"century",
+    u"ampere",
+    u"fahrenheit",
+    u"kelvin",
+    u"celsius",
+    u"arc-second",
+    u"arc-minute",
+    u"degree",
+    u"radian",
+    u"revolution",
+    u"item",
+    u"mole",
+    u"permillion",
+    u"permyriad",
+    u"permille",
+    u"percent",
+    u"karat",
+    u"portion",
+    u"bit",
+    u"byte",
+    u"dot",
+    u"pixel",
+    u"em",
+    u"hertz",
+    u"newton",
+    u"pound-force",
+    u"pascal",
+    u"bar",
+    u"atmosphere",
+    u"ofhg",
+    u"electronvolt",
+    u"dalton",
+    u"joule",
+    u"calorie",
+    u"british-thermal-unit",
+    u"foodcalorie",
+    u"therm-us",
+    u"watt",
+    u"horsepower",
+    u"solar-luminosity",
+    u"volt",
+    u"ohm",
+    u"dunam",
+    u"acre",
+    u"hectare",
+    u"teaspoon",
+    u"tablespoon",
+    u"fluid-ounce-imperial",
+    u"fluid-ounce",
+    u"cup",
+    u"cup-metric",
+    u"pint",
+    u"pint-metric",
+    u"quart",
+    u"liter",
+    u"gallon",
+    u"gallon-imperial",
+    u"bushel",
+    u"barrel",
+    u"knot",
+    u"g-force",
+    u"lux",
+};
+
+icu::UInitOnce gUnitExtrasInitOnce = U_INITONCE_INITIALIZER;
+
+char16_t* kSerializedUnitExtrasStemTrie = nullptr;
+
+UBool U_CALLCONV cleanupUnitExtras() {
+    uprv_free(kSerializedUnitExtrasStemTrie);
+    kSerializedUnitExtrasStemTrie = nullptr;
+    gUnitExtrasInitOnce.reset();
+    return TRUE;
+}
+
+void U_CALLCONV initUnitExtras(UErrorCode& status) {
+    ucln_i18n_registerCleanup(UCLN_I18N_UNIT_EXTRAS, cleanupUnitExtras);
+
+    UCharsTrieBuilder b(status);
+    if (U_FAILURE(status)) { return; }
+
+    // Add SI prefixes
+    for (const auto& siPrefixInfo : gSIPrefixStrings) {
+        UnicodeString uSIPrefix(siPrefixInfo.string, -1, US_INV);
+        b.add(uSIPrefix, siPrefixInfo.value + kSIPrefixOffset, status);
+    }
+    if (U_FAILURE(status)) { return; }
+
+    // Add syntax parts (compound, power prefixes)
+    b.add(u"-per-", COMPOUND_PART_PER, status);
+    b.add(u"-", COMPOUND_PART_TIMES, status);
+    b.add(u"-and-", COMPOUND_PART_PLUS, status);
+    b.add(u"square-", POWER_PART_P2, status);
+    b.add(u"cubic-", POWER_PART_P3, status);
+    b.add(u"p2-", POWER_PART_P2, status);
+    b.add(u"p3-", POWER_PART_P3, status);
+    b.add(u"p4-", POWER_PART_P4, status);
+    b.add(u"p5-", POWER_PART_P5, status);
+    b.add(u"p6-", POWER_PART_P6, status);
+    b.add(u"p7-", POWER_PART_P7, status);
+    b.add(u"p8-", POWER_PART_P8, status);
+    b.add(u"p9-", POWER_PART_P9, status);
+    b.add(u"p10-", POWER_PART_P10, status);
+    b.add(u"p11-", POWER_PART_P11, status);
+    b.add(u"p12-", POWER_PART_P12, status);
+    b.add(u"p13-", POWER_PART_P13, status);
+    b.add(u"p14-", POWER_PART_P14, status);
+    b.add(u"p15-", POWER_PART_P15, status);
+    if (U_FAILURE(status)) { return; }
+
+    // Add sanctioned simple units by offset
+    int32_t simpleUnitOffset = kSimpleUnitOffset;
+    for (auto simpleUnit : gSimpleUnits) {
+        b.add(simpleUnit, simpleUnitOffset++, status);
+    }
+
+    // Build the CharsTrie
+    // TODO: Use SLOW or FAST here?
+    UnicodeString result;
+    b.buildUnicodeString(USTRINGTRIE_BUILD_FAST, result, status);
+    if (U_FAILURE(status)) { return; }
+
+    // Copy the result into the global constant pointer
+    size_t numBytes = result.length() * sizeof(char16_t);
+    kSerializedUnitExtrasStemTrie = static_cast<char16_t*>(uprv_malloc(numBytes));
+    uprv_memcpy(kSerializedUnitExtrasStemTrie, result.getBuffer(), numBytes);
+}
+
+class Token {
+public:
+    Token(int32_t match) : fMatch(match) {}
+
+    enum Type {
+        TYPE_UNDEFINED,
+        TYPE_SI_PREFIX,
+        TYPE_COMPOUND_PART,
+        TYPE_POWER_PART,
+        TYPE_ONE,
+        TYPE_SIMPLE_UNIT,
+    };
+
+    Type getType() const {
+        if (fMatch <= 0) {
+            UPRV_UNREACHABLE;
+        }
+        if (fMatch < kCompoundPartOffset) {
+            return TYPE_SI_PREFIX;
+        }
+        if (fMatch < kPowerPartOffset) {
+            return TYPE_COMPOUND_PART;
+        }
+        if (fMatch < kSimpleUnitOffset) {
+            return TYPE_POWER_PART;
+        }
+        if (fMatch == kSimpleUnitOffset) {
+            return TYPE_ONE;
+        }
+        return TYPE_SIMPLE_UNIT;
+    }
+
+    UMeasureSIPrefix getSIPrefix() const {
+        U_ASSERT(getType() == TYPE_SI_PREFIX);
+        return static_cast<UMeasureSIPrefix>(fMatch - kSIPrefixOffset);
+    }
+
+    int32_t getMatch() const {
+        U_ASSERT(getType() == TYPE_COMPOUND_PART);
+        return fMatch;
+    }
+
+    int8_t getPower() const {
+        U_ASSERT(getType() == TYPE_POWER_PART);
+        return static_cast<int8_t>(fMatch - kPowerPartOffset);
+    }
+
+    int32_t getSimpleUnitIndex() const {
+        U_ASSERT(getType() == TYPE_SIMPLE_UNIT);
+        return fMatch - kSimpleUnitOffset;
+    }
+
+private:
+    int32_t fMatch;
+};
+
+class Parser {
+public:
+    static Parser from(StringPiece source, UErrorCode& status) {
+        if (U_FAILURE(status)) {
+            return Parser();
+        }
+        umtx_initOnce(gUnitExtrasInitOnce, &initUnitExtras, status);
+        if (U_FAILURE(status)) {
+            return Parser();
+        }
+        return Parser(source);
+    }
+
+    MeasureUnitImpl parse(UErrorCode& status) {
+        MeasureUnitImpl result;
+        parseImpl(result, status);
+        return result;
+    }
+
+private:
+    int32_t fIndex = 0;
+    StringPiece fSource;
+    UCharsTrie fTrie;
+
+    bool fAfterPer = false;
+
+    Parser() : fSource(""), fTrie(u"") {}
+
+    Parser(StringPiece source)
+        : fSource(source), fTrie(kSerializedUnitExtrasStemTrie) {}
+
+    inline bool hasNext() const {
+        return fIndex < fSource.length();
+    }
+
+    Token nextToken(UErrorCode& status) {
+        fTrie.reset();
+        int32_t match = -1;
+        int32_t previ = -1;
+        do {
+            auto result = fTrie.next(fSource.data()[fIndex++]);
+            if (result == USTRINGTRIE_NO_MATCH) {
+                break;
+            } else if (result == USTRINGTRIE_NO_VALUE) {
+                continue;
+            }
+            U_ASSERT(USTRINGTRIE_HAS_VALUE(result));
+            match = fTrie.getValue();
+            previ = fIndex;
+            if (result == USTRINGTRIE_FINAL_VALUE) {
+                break;
+            }
+            U_ASSERT(result == USTRINGTRIE_INTERMEDIATE_VALUE);
+            // continue;
+        } while (fIndex < fSource.length());
+
+        if (match < 0) {
+            status = kUnitIdentifierSyntaxError;
+        } else {
+            fIndex = previ;
+        }
+        return Token(match);
+    }
+
+    void nextSingleUnit(SingleUnitImpl& result, bool& sawPlus, UErrorCode& status) {
+        sawPlus = false;
+        if (U_FAILURE(status)) {
+            return;
+        }
+
+        if (!hasNext()) {
+            // probably "one"
+            return;
+        }
+
+        // state:
+        // 0 = no tokens seen yet (will accept power, SI prefix, or simple unit)
+        // 1 = power token seen (will not accept another power token)
+        // 2 = SI prefix token seen (will not accept a power or SI prefix token)
+        int32_t state = 0;
+        int32_t previ = fIndex;
+
+        // Maybe read a compound part
+        if (fIndex != 0) {
+            Token token = nextToken(status);
+            if (U_FAILURE(status)) {
+                return;
+            }
+            if (token.getType() != Token::TYPE_COMPOUND_PART) {
+                status = kUnitIdentifierSyntaxError;
+                return;
+            }
+            switch (token.getMatch()) {
+                case COMPOUND_PART_PER:
+                    if (fAfterPer) {
+                        status = kUnitIdentifierSyntaxError;
+                        return;
+                    }
+                    fAfterPer = true;
+                    result.dimensionality = -1;
+                    break;
+
+                case COMPOUND_PART_TIMES:
+                    break;
+
+                case COMPOUND_PART_PLUS:
+                    sawPlus = true;
+                    fAfterPer = false;
+                    break;
+            }
+            previ = fIndex;
+        }
+
+        // Read a unit
+        while (hasNext()) {
+            Token token = nextToken(status);
+            if (U_FAILURE(status)) {
+                return;
+            }
+
+            switch (token.getType()) {
+                case Token::TYPE_POWER_PART:
+                    if (state > 0) {
+                        status = kUnitIdentifierSyntaxError;
+                        return;
+                    }
+                    result.dimensionality *= token.getPower();
+                    previ = fIndex;
+                    state = 1;
+                    break;
+
+                case Token::TYPE_SI_PREFIX:
+                    if (state > 1) {
+                        status = kUnitIdentifierSyntaxError;
+                        return;
+                    }
+                    result.siPrefix = token.getSIPrefix();
+                    previ = fIndex;
+                    state = 2;
+                    break;
+
+                case Token::TYPE_ONE:
+                    // Skip "one" and go to the next unit
+                    return nextSingleUnit(result, sawPlus, status);
+
+                case Token::TYPE_SIMPLE_UNIT:
+                    result.index = token.getSimpleUnitIndex();
+                    result.identifier = fSource.substr(previ, fIndex - previ);
+                    return;
+
+                default:
+                    status = kUnitIdentifierSyntaxError;
+                    return;
+            }
+        }
+
+        // We ran out of tokens before finding a complete single unit.
+        status = kUnitIdentifierSyntaxError;
+    }
+
+    void parseImpl(MeasureUnitImpl& result, UErrorCode& status) {
+        if (U_FAILURE(status)) {
+            return;
+        }
+        int32_t unitNum = 0;
+        while (hasNext()) {
+            bool sawPlus;
+            SingleUnitImpl singleUnit;
+            nextSingleUnit(singleUnit, sawPlus, status);
+            if (U_FAILURE(status)) {
+                return;
+            }
+            if (singleUnit.index == 0) {
+                continue;
+            }
+            bool added = result.append(singleUnit, status);
+            if (sawPlus && !added) {
+                // Two similar units are not allowed in a sequence unit
+                status = kUnitIdentifierSyntaxError;
+                return;
+            }
+            if ((++unitNum) >= 2) {
+                UMeasureUnitComplexity complexity = sawPlus
+                    ? UMEASURE_UNIT_SEQUENCE
+                    : UMEASURE_UNIT_COMPOUND;
+                if (unitNum == 2) {
+                    U_ASSERT(result.complexity == UMEASURE_UNIT_SINGLE);
+                    result.complexity = complexity;
+                } else if (result.complexity != complexity) {
+                    // Mixed sequence and compound units
+                    status = kUnitIdentifierSyntaxError;
+                    return;
+                }
+            }
+        }
+    }
+};
+
+int32_t U_CALLCONV
+compareSingleUnits(const void* /*context*/, const void* left, const void* right) {
+    auto realLeft = static_cast<const SingleUnitImpl* const*>(left);
+    auto realRight = static_cast<const SingleUnitImpl* const*>(right);
+    return (*realLeft)->compareTo(**realRight);
+}
+
+/**
+ * Generate the identifier string for a single unit in place.
+ */
+void serializeSingle(const SingleUnitImpl& singleUnit, bool first, CharString& output, UErrorCode& status) {
+    if (first && singleUnit.dimensionality < 0) {
+        output.append("one-per-", status);
+    }
+
+    if (singleUnit.index == 0) {
+        // Don't propagate SI prefixes and powers on one
+        output.append("one", status);
+        return;
+    }
+    int8_t posPower = std::abs(singleUnit.dimensionality);
+    if (posPower == 0) {
+        status = U_INTERNAL_PROGRAM_ERROR;
+    } else if (posPower == 1) {
+        // no-op
+    } else if (posPower == 2) {
+        output.append("square-", status);
+    } else if (posPower == 3) {
+        output.append("cubic-", status);
+    } else if (posPower < 10) {
+        output.append('p', status);
+        output.append(posPower + '0', status);
+        output.append('-', status);
+    } else if (posPower <= 15) {
+        output.append("p1", status);
+        output.append('0' + (posPower % 10), status);
+        output.append('-', status);
+    } else {
+        status = kUnitIdentifierSyntaxError;
+    }
+    if (U_FAILURE(status)) {
+        return;
+    }
+
+    if (singleUnit.siPrefix != UMEASURE_SI_PREFIX_ONE) {
+        for (const auto& siPrefixInfo : gSIPrefixStrings) {
+            if (siPrefixInfo.value == singleUnit.siPrefix) {
+                output.append(siPrefixInfo.string, status);
+                break;
+            }
+        }
+    }
+    if (U_FAILURE(status)) {
+        return;
+    }
+
+    output.append(singleUnit.identifier, status);
+}
+
+/**
+ * Normalize a MeasureUnitImpl and generate the identifier string in place.
+ */
+void serialize(MeasureUnitImpl& impl, UErrorCode& status) {
+    if (U_FAILURE(status)) {
+        return;
+    }
+    U_ASSERT(impl.identifier.isEmpty());
+    if (impl.units.length() == 0) {
+        impl.identifier.append("one", status);
+        return;
+    }
+    if (impl.complexity == UMEASURE_UNIT_COMPOUND) {
+        // Note: don't sort a SEQUENCE unit
+        uprv_sortArray(
+            impl.units.getAlias(),
+            impl.units.length(),
+            sizeof(impl.units[0]),
+            compareSingleUnits,
+            nullptr,
+            false,
+            &status);
+        if (U_FAILURE(status)) {
+            return;
+        }
+    }
+    serializeSingle(*impl.units[0], true, impl.identifier, status);
+    if (impl.units.length() == 1) {
+        return;
+    }
+    for (int32_t i = 1; i < impl.units.length(); i++) {
+        const SingleUnitImpl& prev = *impl.units[i-1];
+        const SingleUnitImpl& curr = *impl.units[i];
+        if (impl.complexity == UMEASURE_UNIT_SEQUENCE) {
+            impl.identifier.append("-and-", status);
+            serializeSingle(curr, true, impl.identifier, status);
+        } else {
+            if (prev.dimensionality > 0 && curr.dimensionality < 0) {
+                impl.identifier.append("-per-", status);
+            } else {
+                impl.identifier.append('-', status);
+            }
+            serializeSingle(curr, false, impl.identifier, status);
+        }
+    }
+
+}
+
+/** @return true if a new item was added */
+bool appendImpl(MeasureUnitImpl& impl, const SingleUnitImpl& unit, UErrorCode& status) {
+    // Find a similar unit that already exists, to attempt to coalesce
+    SingleUnitImpl* oldUnit = nullptr;
+    for (int32_t i = 0; i < impl.units.length(); i++) {
+        auto* candidate = impl.units[i];
+        if (candidate->isCompatibleWith(unit)) {
+            oldUnit = candidate;
+        }
+    }
+    if (oldUnit) {
+        oldUnit->dimensionality += unit.dimensionality;
+    } else {
+        SingleUnitImpl* destination = impl.units.emplaceBack();
+        if (!destination) {
+            status = U_MEMORY_ALLOCATION_ERROR;
+            return false;
+        }
+        *destination = unit;
+    }
+    return (oldUnit == nullptr);
+}
+
+} // namespace
+
+
+SingleUnitImpl SingleUnitImpl::forMeasureUnit(const MeasureUnit& measureUnit, UErrorCode& status) {
+    MeasureUnitImpl temp;
+    const MeasureUnitImpl& impl = MeasureUnitImpl::forMeasureUnit(measureUnit, temp, status);
+    if (U_FAILURE(status)) {
+        return {};
+    }
+    if (impl.units.length() == 0) {
+        return {};
+    }
+    if (impl.units.length() == 1) {
+        return *impl.units[0];
+    }
+    status = U_ILLEGAL_ARGUMENT_ERROR;
+    return {};
+}
+
+MeasureUnit SingleUnitImpl::build(UErrorCode& status) const {
+    MeasureUnitImpl temp;
+    temp.append(*this, status);
+    return std::move(temp).build(status);
+}
+
+
+MeasureUnitImpl MeasureUnitImpl::forIdentifier(StringPiece identifier, UErrorCode& status) {
+    return Parser::from(identifier, status).parse(status);
+}
+
+const MeasureUnitImpl& MeasureUnitImpl::forMeasureUnit(
+        const MeasureUnit& measureUnit, MeasureUnitImpl& memory, UErrorCode& status) {
+    if (measureUnit.fImpl) {
+        return *measureUnit.fImpl;
+    } else {
+        memory = Parser::from(measureUnit.getIdentifier(), status).parse(status);
+        return memory;
+    }
+}
+
+MeasureUnitImpl MeasureUnitImpl::forMeasureUnitMaybeCopy(
+        const MeasureUnit& measureUnit, UErrorCode& status) {
+    if (measureUnit.fImpl) {
+        return measureUnit.fImpl->copy(status);
+    } else {
+        return Parser::from(measureUnit.getIdentifier(), status).parse(status);
+    }
+}
+
+void MeasureUnitImpl::takeReciprocal(UErrorCode& /*status*/) {
+    identifier.clear();
+    for (int32_t i = 0; i < units.length(); i++) {
+        units[i]->dimensionality *= -1;
+    }
+}
+
+bool MeasureUnitImpl::append(const SingleUnitImpl& singleUnit, UErrorCode& status) {
+    identifier.clear();
+    return appendImpl(*this, singleUnit, status);
+}
+
+MeasureUnit MeasureUnitImpl::build(UErrorCode& status) && {
+    serialize(*this, status);
+    return MeasureUnit(std::move(*this));
+}
+
+
+MeasureUnit MeasureUnit::forIdentifier(StringPiece identifier, UErrorCode& status) {
+    return Parser::from(identifier, status).parse(status).build(status);
+}
+
+UMeasureUnitComplexity MeasureUnit::getComplexity(UErrorCode& status) const {
+    MeasureUnitImpl temp;
+    return MeasureUnitImpl::forMeasureUnit(*this, temp, status).complexity;
+}
+
+UMeasureSIPrefix MeasureUnit::getSIPrefix(UErrorCode& status) const {
+    return SingleUnitImpl::forMeasureUnit(*this, status).siPrefix;
+}
+
+MeasureUnit MeasureUnit::withSIPrefix(UMeasureSIPrefix prefix, UErrorCode& status) const {
+    SingleUnitImpl singleUnit = SingleUnitImpl::forMeasureUnit(*this, status);
+    singleUnit.siPrefix = prefix;
+    return singleUnit.build(status);
+}
+
+int32_t MeasureUnit::getDimensionality(UErrorCode& status) const {
+    return SingleUnitImpl::forMeasureUnit(*this, status).dimensionality;
+}
+
+MeasureUnit MeasureUnit::withDimensionality(int32_t dimensionality, UErrorCode& status) const {
+    SingleUnitImpl singleUnit = SingleUnitImpl::forMeasureUnit(*this, status);
+    singleUnit.dimensionality = dimensionality;
+    return singleUnit.build(status);
+}
+
+MeasureUnit MeasureUnit::reciprocal(UErrorCode& status) const {
+    MeasureUnitImpl impl = MeasureUnitImpl::forMeasureUnitMaybeCopy(*this, status);
+    impl.takeReciprocal(status);
+    return std::move(impl).build(status);
+}
+
+MeasureUnit MeasureUnit::product(const MeasureUnit& other, UErrorCode& status) const {
+    MeasureUnitImpl impl = MeasureUnitImpl::forMeasureUnitMaybeCopy(*this, status);
+    MeasureUnitImpl temp;
+    const MeasureUnitImpl& otherImpl = MeasureUnitImpl::forMeasureUnit(other, temp, status);
+    if (impl.complexity == UMEASURE_UNIT_SEQUENCE || otherImpl.complexity == UMEASURE_UNIT_SEQUENCE) {
+        status = U_ILLEGAL_ARGUMENT_ERROR;
+        return {};
+    }
+    for (int32_t i = 0; i < otherImpl.units.length(); i++) {
+        impl.append(*otherImpl.units[i], status);
+    }
+    if (impl.units.length() > 1) {
+        impl.complexity = UMEASURE_UNIT_COMPOUND;
+    }
+    return std::move(impl).build(status);
+}
+
+LocalArray<MeasureUnit> MeasureUnit::splitToSingleUnits(int32_t& outCount, UErrorCode& status) const {
+    MeasureUnitImpl temp;
+    const MeasureUnitImpl& impl = MeasureUnitImpl::forMeasureUnit(*this, temp, status);
+    outCount = impl.units.length();
+    MeasureUnit* arr = new MeasureUnit[outCount];
+    for (int32_t i = 0; i < outCount; i++) {
+        arr[i] = impl.units[i]->build(status);
+    }
+    return LocalArray<MeasureUnit>(arr, status);
+}
+
+
+U_NAMESPACE_END
+
+#endif /* !UNCONFIG_NO_FORMATTING */
diff --git a/icu4c/source/i18n/measunit_impl.h b/icu4c/source/i18n/measunit_impl.h
new file mode 100644
index 0000000..5d2e6b1
--- /dev/null
+++ b/icu4c/source/i18n/measunit_impl.h
@@ -0,0 +1,173 @@
+// © 2020 and later: Unicode, Inc. and others.
+// License & terms of use: http://www.unicode.org/copyright.html
+
+#ifndef __MEASUNIT_IMPL_H__
+#define __MEASUNIT_IMPL_H__
+
+#include "unicode/utypes.h"
+
+#if !UCONFIG_NO_FORMATTING
+
+#include "unicode/measunit.h"
+#include "cmemory.h"
+#include "charstr.h"
+
+U_NAMESPACE_BEGIN
+
+
+static const char16_t kDefaultCurrency[] = u"XXX";
+static const char kDefaultCurrency8[] = "XXX";
+
+
+/**
+ * A struct representing a single unit (optional SI prefix and dimensionality).
+ */
+struct SingleUnitImpl : public UMemory {
+    /**
+     * Gets a single unit from the MeasureUnit. If there are multiple single units, sets an error
+     * code and return the base dimensionless unit. Parses if necessary.
+     */
+    static SingleUnitImpl forMeasureUnit(const MeasureUnit& measureUnit, UErrorCode& status);
+
+    /** Transform this SingleUnitImpl into a MeasureUnit, simplifying if possible. */
+    MeasureUnit build(UErrorCode& status) const;
+
+    /** Compare this SingleUnitImpl to another SingleUnitImpl. */
+    int32_t compareTo(const SingleUnitImpl& other) const {
+        if (dimensionality < 0 && other.dimensionality > 0) {
+            // Positive dimensions first
+            return 1;
+        }
+        if (dimensionality > 0 && other.dimensionality < 0) {
+            return -1;
+        }
+        if (index < other.index) {
+            return -1;
+        }
+        if (index > other.index) {
+            return 1;
+        }
+        if (siPrefix < other.siPrefix) {
+            return -1;
+        }
+        if (siPrefix > other.siPrefix) {
+            return 1;
+        }
+        return 0;
+    }
+
+    /**
+     * Return whether this SingleUnitImpl is compatible with another for the purpose of coalescing.
+     *
+     * Units with the same base unit and SI prefix should match, except that they must also have
+     * the same dimensionality sign, such that we don't merge numerator and denominator.
+     */
+    bool isCompatibleWith(const SingleUnitImpl& other) const {
+        return (compareTo(other) == 0);
+    }
+
+    /** Simple unit index, unique for every simple unit. */
+    int32_t index = 0;
+
+    /** Simple unit identifier; memory not owned by the SimpleUnit. */
+    StringPiece identifier;
+
+    /** SI prefix. **/
+    UMeasureSIPrefix siPrefix = UMEASURE_SI_PREFIX_ONE;
+    
+    /** Dimensionality. **/
+    int32_t dimensionality = 1;
+};
+
+
+/**
+ * Internal representation of measurement units. Capable of representing all complexities of units,
+ * including sequence and compound units.
+ */
+struct MeasureUnitImpl : public UMemory {
+    /** Extract the MeasureUnitImpl from a MeasureUnit. */
+    static inline const MeasureUnitImpl* get(const MeasureUnit& measureUnit) {
+        return measureUnit.fImpl;
+    }
+
+    /**
+     * Parse a unit identifier into a MeasureUnitImpl.
+     *
+     * @param identifier The unit identifier string.
+     * @param status Set if the identifier string is not valid.
+     * @return A newly parsed value object.
+     */
+    static MeasureUnitImpl forIdentifier(StringPiece identifier, UErrorCode& status);
+
+    /**
+     * Extract the MeasureUnitImpl from a MeasureUnit, or parse if it is not present.
+     * 
+     * @param measureUnit The source MeasureUnit.
+     * @param memory A place to write the new MeasureUnitImpl if parsing is required.
+     * @param status Set if an error occurs.
+     * @return A reference to either measureUnit.fImpl or memory.
+     */
+    static const MeasureUnitImpl& forMeasureUnit(
+        const MeasureUnit& measureUnit, MeasureUnitImpl& memory, UErrorCode& status);
+
+    /**
+     * Extract the MeasureUnitImpl from a MeasureUnit, or parse if it is not present.
+     *
+     * @param measureUnit The source MeasureUnit.
+     * @param status Set if an error occurs.
+     * @return A value object, either newly parsed or copied from measureUnit.
+     */
+    static MeasureUnitImpl forMeasureUnitMaybeCopy(
+        const MeasureUnit& measureUnit, UErrorCode& status);
+
+    /**
+     * Used for currency units.
+     */
+    static inline MeasureUnitImpl forCurrencyCode(StringPiece currencyCode) {
+        MeasureUnitImpl result;
+        UErrorCode localStatus = U_ZERO_ERROR;
+        result.identifier.append(currencyCode, localStatus);
+        // localStatus is not expected to fail since currencyCode should be 3 chars long
+        return result;
+    }
+
+    /** Transform this MeasureUnitImpl into a MeasureUnit, simplifying if possible. */
+    MeasureUnit build(UErrorCode& status) &&;
+
+    /**
+     * Create a copy of this MeasureUnitImpl. Don't use copy constructor to make this explicit.
+     */
+    inline MeasureUnitImpl copy(UErrorCode& status) const {
+        MeasureUnitImpl result;
+        result.complexity = complexity;
+        result.units.appendAll(units, status);
+        result.identifier.append(identifier, status);
+        return result;
+    }
+
+    /** Mutates this MeasureUnitImpl to take the reciprocal. */
+    void takeReciprocal(UErrorCode& status);
+
+    /** Mutates this MeasureUnitImpl to append a single unit. */
+    bool append(const SingleUnitImpl& singleUnit, UErrorCode& status);
+
+    /** The complexity, either SINGLE, COMPOUND, or SEQUENCE. */
+    UMeasureUnitComplexity complexity = UMEASURE_UNIT_SINGLE;
+
+    /**
+     * The list of simple units. These may be summed or multiplied, based on the value of the
+     * complexity field.
+     */
+    MaybeStackVector<SingleUnitImpl> units;
+
+    /**
+     * The full unit identifier.  Owned by the MeasureUnitImpl.  Empty if not computed.
+     */
+    CharString identifier;
+};
+
+
+U_NAMESPACE_END
+
+#endif /* #if !UCONFIG_NO_FORMATTING */
+#endif //__MEASUNIT_IMPL_H__
diff --git a/icu4c/source/i18n/nounit.cpp b/icu4c/source/i18n/nounit.cpp
index 076f76f..b993cb5 100644
--- a/icu4c/source/i18n/nounit.cpp
+++ b/icu4c/source/i18n/nounit.cpp
@@ -11,7 +11,7 @@
 UOBJECT_DEFINE_RTTI_IMPLEMENTATION(NoUnit)
 
 NoUnit U_EXPORT2 NoUnit::base() {
-    return NoUnit("base");
+    return NoUnit("one");
 }
 
 NoUnit U_EXPORT2 NoUnit::percent() {
diff --git a/icu4c/source/i18n/number_asformat.cpp b/icu4c/source/i18n/number_asformat.cpp
index e876174..9d10d1f 100644
--- a/icu4c/source/i18n/number_asformat.cpp
+++ b/icu4c/source/i18n/number_asformat.cpp
@@ -102,4 +102,16 @@
     return fFormatter;
 }
 
+
+// Definitions of public API methods (put here for dependency disentanglement)
+
+Format* LocalizedNumberFormatter::toFormat(UErrorCode& status) const {
+    if (U_FAILURE(status)) {
+        return nullptr;
+    }
+    LocalPointer<LocalizedNumberFormatterAsFormat> retval(
+            new LocalizedNumberFormatterAsFormat(*this, fMacros.locale), status);
+    return retval.orphan();
+}
+
 #endif /* #if !UCONFIG_NO_FORMATTING */
diff --git a/icu4c/source/i18n/number_fluent.cpp b/icu4c/source/i18n/number_fluent.cpp
index 2dbd2fa..9cdb8b7 100644
--- a/icu4c/source/i18n/number_fluent.cpp
+++ b/icu4c/source/i18n/number_fluent.cpp
@@ -11,7 +11,6 @@
 #include "number_formatimpl.h"
 #include "umutex.h"
 #include "number_asformat.h"
-#include "number_skeletons.h"
 #include "number_utils.h"
 #include "number_utypes.h"
 #include "util.h"
@@ -21,6 +20,16 @@
 using namespace icu::number;
 using namespace icu::number::impl;
 
+#if (U_PF_WINDOWS <= U_PLATFORM && U_PLATFORM <= U_PF_CYGWIN) && defined(_MSC_VER)
+// Ignore MSVC warning 4661. This is generated for NumberFormatterSettings<>::toSkeleton() as this method
+// is defined elsewhere (in number_skeletons.cpp). The compiler is warning that the explicit template instantiation
+// inside this single translation unit (CPP file) is incomplete, and thus it isn't sure if the template class is
+// fully defined. However, since each translation unit explicitly instantiates all the necessary template classes,
+// they will all be passed to the linker, and the linker will still find and export all the class members.
+#pragma warning(push)
+#pragma warning(disable: 4661)
+#endif
+
 template<typename Derived>
 Derived NumberFormatterSettings<Derived>::notation(const Notation& notation) const& {
     Derived copy(*this);
@@ -320,16 +329,7 @@
     return move;
 }
 
-template<typename Derived>
-UnicodeString NumberFormatterSettings<Derived>::toSkeleton(UErrorCode& status) const {
-    if (U_FAILURE(status)) {
-        return ICU_Utility::makeBogusString();
-    }
-    if (fMacros.copyErrorTo(status)) {
-        return ICU_Utility::makeBogusString();
-    }
-    return skeleton::generate(fMacros, status);
-}
+// Note: toSkeleton defined in number_skeletons.cpp
 
 template<typename Derived>
 LocalPointer<Derived> NumberFormatterSettings<Derived>::clone() const & {
@@ -358,15 +358,7 @@
     return with().locale(locale);
 }
 
-UnlocalizedNumberFormatter
-NumberFormatter::forSkeleton(const UnicodeString& skeleton, UErrorCode& status) {
-    return skeleton::create(skeleton, nullptr, status);
-}
-
-UnlocalizedNumberFormatter
-NumberFormatter::forSkeleton(const UnicodeString& skeleton, UParseError& perror, UErrorCode& status) {
-    return skeleton::create(skeleton, &perror, status);
-}
+// Note: forSkeleton defined in number_skeletons.cpp
 
 
 template<typename T> using NFS = NumberFormatterSettings<T>;
@@ -766,14 +758,11 @@
     return umtx_loadAcquire(*callCount);
 }
 
-Format* LocalizedNumberFormatter::toFormat(UErrorCode& status) const {
-    if (U_FAILURE(status)) {
-        return nullptr;
-    }
-    LocalPointer<LocalizedNumberFormatterAsFormat> retval(
-            new LocalizedNumberFormatterAsFormat(*this, fMacros.locale), status);
-    return retval.orphan();
-}
+// Note: toFormat defined in number_asformat.cpp
 
+#if (U_PF_WINDOWS <= U_PLATFORM && U_PLATFORM <= U_PF_CYGWIN) && defined(_MSC_VER)
+// Warning 4661.
+#pragma warning(pop)
+#endif
 
 #endif /* #if !UCONFIG_NO_FORMATTING */
diff --git a/icu4c/source/i18n/number_longnames.cpp b/icu4c/source/i18n/number_longnames.cpp
index 5378eda..74ee0ef 100644
--- a/icu4c/source/i18n/number_longnames.cpp
+++ b/icu4c/source/i18n/number_longnames.cpp
@@ -188,6 +188,12 @@
 LongNameHandler::forMeasureUnit(const Locale &loc, const MeasureUnit &unitRef, const MeasureUnit &perUnit,
                                 const UNumberUnitWidth &width, const PluralRules *rules,
                                 const MicroPropsGenerator *parent, UErrorCode &status) {
+    if (uprv_strlen(unitRef.getType()) == 0 || uprv_strlen(perUnit.getType()) == 0) {
+        // TODO(ICU-20941): Unsanctioned unit. Not yet fully supported. Set an error code.
+        status = U_UNSUPPORTED_ERROR;
+        return nullptr;
+    }
+
     MeasureUnit unit = unitRef;
     if (uprv_strcmp(perUnit.getType(), "none") != 0) {
         // Compound unit: first try to simplify (e.g., meters per second is its own unit).
diff --git a/icu4c/source/i18n/number_skeletons.cpp b/icu4c/source/i18n/number_skeletons.cpp
index e186a56..5b0fe2b 100644
--- a/icu4c/source/i18n/number_skeletons.cpp
+++ b/icu4c/source/i18n/number_skeletons.cpp
@@ -22,6 +22,8 @@
 #include "charstr.h"
 #include "string_segment.h"
 #include "unicode/errorcode.h"
+#include "util.h"
+#include "measunit_impl.h"
 
 using namespace icu;
 using namespace icu::number;
@@ -1036,12 +1038,23 @@
     SKELETON_UCHAR_TO_CHAR(buffer, segment.toTempUnicodeString(), 0, segment.length(), status);
 
     ErrorCode internalStatus;
-    MeasureUnit::parseCoreUnitIdentifier(buffer.toStringPiece(), &macros.unit, &macros.perUnit, internalStatus);
+    auto fullUnit = MeasureUnitImpl::forIdentifier(buffer.toStringPiece(), internalStatus);
     if (internalStatus.isFailure()) {
         // throw new SkeletonSyntaxException("Invalid core unit identifier", segment, e);
         status = U_NUMBER_SKELETON_SYNTAX_ERROR;
         return;
     }
+
+    // TODO(ICU-20941): Clean this up.
+    for (int32_t i = 0; i < fullUnit.units.length(); i++) {
+        SingleUnitImpl* subUnit = fullUnit.units[i];
+        if (subUnit->dimensionality > 0) {
+            macros.unit = macros.unit.product(subUnit->build(status), status);
+        } else {
+            subUnit->dimensionality *= -1;
+            macros.perUnit = macros.perUnit.product(subUnit->build(status), status);
+        }
+    }
 }
 
 void blueprint_helpers::parseFractionStem(const StringSegment& segment, MacroProps& macros,
@@ -1670,4 +1683,49 @@
 }
 
 
+// Definitions of public API methods (put here for dependency disentanglement)
+
+#if (U_PF_WINDOWS <= U_PLATFORM && U_PLATFORM <= U_PF_CYGWIN) && defined(_MSC_VER)
+// Ignore MSVC warning 4661. This is generated for NumberFormatterSettings<>::toSkeleton() as this method
+// is defined elsewhere (in number_skeletons.cpp). The compiler is warning that the explicit template instantiation
+// inside this single translation unit (CPP file) is incomplete, and thus it isn't sure if the template class is
+// fully defined. However, since each translation unit explicitly instantiates all the necessary template classes,
+// they will all be passed to the linker, and the linker will still find and export all the class members.
+#pragma warning(push)
+#pragma warning(disable: 4661)
+#endif
+
+template<typename Derived>
+UnicodeString NumberFormatterSettings<Derived>::toSkeleton(UErrorCode& status) const {
+    if (U_FAILURE(status)) {
+        return ICU_Utility::makeBogusString();
+    }
+    if (fMacros.copyErrorTo(status)) {
+        return ICU_Utility::makeBogusString();
+    }
+    return skeleton::generate(fMacros, status);
+}
+
+// Declare all classes that implement NumberFormatterSettings
+// See https://stackoverflow.com/a/495056/1407170
+template
+class icu::number::NumberFormatterSettings<icu::number::UnlocalizedNumberFormatter>;
+template
+class icu::number::NumberFormatterSettings<icu::number::LocalizedNumberFormatter>;
+
+UnlocalizedNumberFormatter
+NumberFormatter::forSkeleton(const UnicodeString& skeleton, UErrorCode& status) {
+    return skeleton::create(skeleton, nullptr, status);
+}
+
+UnlocalizedNumberFormatter
+NumberFormatter::forSkeleton(const UnicodeString& skeleton, UParseError& perror, UErrorCode& status) {
+    return skeleton::create(skeleton, &perror, status);
+}
+
+#if (U_PF_WINDOWS <= U_PLATFORM && U_PLATFORM <= U_PF_CYGWIN) && defined(_MSC_VER)
+// Warning 4661.
+#pragma warning(pop)
+#endif
+
 #endif /* #if !UCONFIG_NO_FORMATTING */
diff --git a/icu4c/source/i18n/ucln_in.h b/icu4c/source/i18n/ucln_in.h
index 2f70a85..765cdd5 100644
--- a/icu4c/source/i18n/ucln_in.h
+++ b/icu4c/source/i18n/ucln_in.h
@@ -26,6 +26,7 @@
 It's usually best to have child dependencies called first. */
 typedef enum ECleanupI18NType {
     UCLN_I18N_START = -1,
+    UCLN_I18N_UNIT_EXTRAS,
     UCLN_I18N_NUMBER_SKELETONS,
     UCLN_I18N_CURRENCY_SPACING,
     UCLN_I18N_SPOOF,
diff --git a/icu4c/source/i18n/unicode/measunit.h b/icu4c/source/i18n/unicode/measunit.h
index 31c93c0..9353159 100644
--- a/icu4c/source/i18n/unicode/measunit.h
+++ b/icu4c/source/i18n/unicode/measunit.h
@@ -20,6 +20,7 @@
 #if !UCONFIG_NO_FORMATTING
 
 #include "unicode/unistr.h"
+#include "unicode/localpointer.h"
 
 /**
  * \file 
@@ -29,6 +30,202 @@
 U_NAMESPACE_BEGIN
 
 class StringEnumeration;
+struct MeasureUnitImpl;
+
+#ifndef U_HIDE_DRAFT_API
+/**
+ * Enumeration for unit complexity. There are three levels:
+ * 
+ * - SINGLE: A single unit, optionally with a power and/or SI prefix. Examples: hectare,
+ *           square-kilometer, kilojoule, one-per-second.
+ * - COMPOUND: A unit composed of the product of multiple single units. Examples:
+ *             meter-per-second, kilowatt-hour, kilogram-meter-per-square-second.
+ * - SEQUENCE: A unit composed of the sum of multiple single units. Examples: foot+inch,
+ *             hour+minute+second, degree+arcminute+arcsecond.
+ *
+ * The complexity determines which operations are available. For example, you cannot set the power
+ * or SI prefix of a compound unit.
+ *
+ * @draft ICU 67
+ */
+enum UMeasureUnitComplexity {
+    /**
+     * A single unit, like kilojoule.
+     *
+     * @draft ICU 67
+     */
+    UMEASURE_UNIT_SINGLE,
+
+    /**
+     * A compound unit, like meter-per-second.
+     * 
+     * @draft ICU 67
+     */
+    UMEASURE_UNIT_COMPOUND,
+
+    /**
+     * A sequence unit, like hour+minute.
+     *
+     * @draft ICU 67
+     */
+    UMEASURE_UNIT_SEQUENCE
+};
+
+/**
+ * Enumeration for SI prefixes, such as "kilo".
+ *
+ * @draft ICU 67
+ */
+typedef enum UMeasureSIPrefix {
+
+    /**
+     * SI prefix: yotta, 10^24.
+     *
+     * @draft ICU 67
+     */
+    UMEASURE_SI_PREFIX_YOTTA = 24,
+
+    /**
+     * SI prefix: zetta, 10^21.
+     *
+     * @draft ICU 67
+     */
+    UMEASURE_SI_PREFIX_ZETTA = 21,
+
+    /**
+     * SI prefix: exa, 10^18.
+     *
+     * @draft ICU 67
+     */
+    UMEASURE_SI_PREFIX_EXA = 18,
+
+    /**
+     * SI prefix: peta, 10^15.
+     *
+     * @draft ICU 67
+     */
+    UMEASURE_SI_PREFIX_PETA = 15,
+
+    /**
+     * SI prefix: tera, 10^12.
+     *
+     * @draft ICU 67
+     */
+    UMEASURE_SI_PREFIX_TERA = 12,
+
+    /**
+     * SI prefix: giga, 10^9.
+     *
+     * @draft ICU 67
+     */
+    UMEASURE_SI_PREFIX_GIGA = 9,
+
+    /**
+     * SI prefix: mega, 10^6.
+     *
+     * @draft ICU 67
+     */
+    UMEASURE_SI_PREFIX_MEGA = 6,
+
+    /**
+     * SI prefix: kilo, 10^3.
+     *
+     * @draft ICU 67
+     */
+    UMEASURE_SI_PREFIX_KILO = 3,
+
+    /**
+     * SI prefix: hecto, 10^2.
+     *
+     * @draft ICU 67
+     */
+    UMEASURE_SI_PREFIX_HECTO = 2,
+
+    /**
+     * SI prefix: deka, 10^1.
+     *
+     * @draft ICU 67
+     */
+    UMEASURE_SI_PREFIX_DEKA = 1,
+
+    /**
+     * The absence of an SI prefix.
+     *
+     * @draft ICU 67
+     */
+    UMEASURE_SI_PREFIX_ONE = 0,
+
+    /**
+     * SI prefix: deci, 10^-1.
+     *
+     * @draft ICU 67
+     */
+    UMEASURE_SI_PREFIX_DECI = -1,
+
+    /**
+     * SI prefix: centi, 10^-2.
+     *
+     * @draft ICU 67
+     */
+    UMEASURE_SI_PREFIX_CENTI = -2,
+
+    /**
+     * SI prefix: milli, 10^-3.
+     *
+     * @draft ICU 67
+     */
+    UMEASURE_SI_PREFIX_MILLI = -3,
+
+    /**
+     * SI prefix: micro, 10^-6.
+     *
+     * @draft ICU 67
+     */
+    UMEASURE_SI_PREFIX_MICRO = -6,
+
+    /**
+     * SI prefix: nano, 10^-9.
+     *
+     * @draft ICU 67
+     */
+    UMEASURE_SI_PREFIX_NANO = -9,
+
+    /**
+     * SI prefix: pico, 10^-12.
+     *
+     * @draft ICU 67
+     */
+    UMEASURE_SI_PREFIX_PICO = -12,
+
+    /**
+     * SI prefix: femto, 10^-15.
+     *
+     * @draft ICU 67
+     */
+    UMEASURE_SI_PREFIX_FEMTO = -15,
+
+    /**
+     * SI prefix: atto, 10^-18.
+     *
+     * @draft ICU 67
+     */
+    UMEASURE_SI_PREFIX_ATTO = -18,
+
+    /**
+     * SI prefix: zepto, 10^-21.
+     *
+     * @draft ICU 67
+     */
+    UMEASURE_SI_PREFIX_ZEPTO = -21,
+
+    /**
+     * SI prefix: yocto, 10^-24.
+     *
+     * @draft ICU 67
+     */
+    UMEASURE_SI_PREFIX_YOCTO = -24
+} UMeasureSIPrefix;
+#endif // U_HIDE_DRAFT_API
 
 /**
  * A unit such as length, mass, volume, currency, etc.  A unit is
@@ -52,13 +249,43 @@
      * @stable ICU 3.0
      */
     MeasureUnit(const MeasureUnit &other);
-        
+
+#ifndef U_HIDE_DRAFT_API
     /**
-     * Assignment operator.
+     * Move constructor.
+     * @draft ICU 67
+     */
+    MeasureUnit(MeasureUnit &&other) noexcept;
+
+    /**
+     * Construct a MeasureUnit from a CLDR Sequence Unit Identifier, defined in UTS 35.
+     * Validates and canonicalizes the identifier.
+     *
+     * <pre>
+     * MeasureUnit example = MeasureUnit::forIdentifier("furlong-per-nanosecond")
+     * </pre>
+     *
+     * @param identifier The CLDR Sequence Unit Identifier
+     * @param status Set if the identifier is invalid.
+     * @draft ICU 67
+     */
+    static MeasureUnit forIdentifier(StringPiece identifier, UErrorCode& status);
+#endif // U_HIDE_DRAFT_API
+
+    /**
+     * Copy assignment operator.
      * @stable ICU 3.0
      */
     MeasureUnit &operator=(const MeasureUnit &other);
 
+#ifndef U_HIDE_DRAFT_API
+    /**
+     * Move assignment operator.
+     * @draft ICU 67
+     */
+    MeasureUnit &operator=(MeasureUnit &&other) noexcept;
+#endif // U_HIDE_DRAFT_API
+
     /**
      * Returns a polymorphic clone of this object.  The result will
      * have the same class as returned by getDynamicClassID().
@@ -90,16 +317,152 @@
 
     /**
      * Get the type.
+     *
+     * If the unit does not have a type, the empty string is returned.
+     *
      * @stable ICU 53
      */
     const char *getType() const;
 
     /**
      * Get the sub type.
+     *
+     * If the unit does not have a subtype, the empty string is returned.
+     *
      * @stable ICU 53
      */
     const char *getSubtype() const;
 
+#ifndef U_HIDE_DRAFT_API
+    /**
+     * Get the CLDR Sequence Unit Identifier for this MeasureUnit, as defined in UTS 35.
+     *
+     * @return The string form of this unit, owned by this MeasureUnit.
+     * @draft ICU 67
+     */
+    const char* getIdentifier() const;
+
+    /**
+     * Compute the complexity of the unit. See UMeasureUnitComplexity for more information.
+     *
+     * @param status Set if an error occurs.
+     * @return The unit complexity.
+     * @draft ICU 67
+     */
+    UMeasureUnitComplexity getComplexity(UErrorCode& status) const;
+
+    /**
+     * Creates a MeasureUnit which is this SINGLE unit augmented with the specified SI prefix.
+     * For example, UMEASURE_SI_PREFIX_KILO for "kilo".
+     *
+     * There is sufficient locale data to format all standard SI prefixes.
+     *
+     * NOTE: Only works on SINGLE units. If this is a COMPOUND or SEQUENCE unit, an error will
+     * occur. For more information, see UMeasureUnitComplexity.
+     *
+     * @param prefix The SI prefix, from UMeasureSIPrefix.
+     * @param status Set if this is not a SINGLE unit or if another error occurs.
+     * @return A new SINGLE unit.
+     * @draft ICU 67
+     */
+    MeasureUnit withSIPrefix(UMeasureSIPrefix prefix, UErrorCode& status) const;
+
+    /**
+     * Gets the current SI prefix of this SINGLE unit. For example, if the unit has the SI prefix
+     * "kilo", then UMEASURE_SI_PREFIX_KILO is returned.
+     *
+     * NOTE: Only works on SINGLE units. If this is a COMPOUND or SEQUENCE unit, an error will
+     * occur. For more information, see UMeasureUnitComplexity.
+     *
+     * @param status Set if this is not a SINGLE unit or if another error occurs.
+     * @return The SI prefix of this SINGLE unit, from UMeasureSIPrefix.
+     * @draft ICU 67
+     */
+    UMeasureSIPrefix getSIPrefix(UErrorCode& status) const;
+
+    /**
+     * Creates a MeasureUnit which is this SINGLE unit augmented with the specified dimensionality
+     * (power). For example, if dimensionality is 2, the unit will be squared.
+     *
+     * NOTE: Only works on SINGLE units. If this is a COMPOUND or SEQUENCE unit, an error will
+     * occur. For more information, see UMeasureUnitComplexity.
+     *
+     * @param dimensionality The dimensionality (power).
+     * @param status Set if this is not a SINGLE unit or if another error occurs.
+     * @return A new SINGLE unit.
+     * @draft ICU 67
+     */
+    MeasureUnit withDimensionality(int32_t dimensionality, UErrorCode& status) const;
+
+    /**
+     * Gets the dimensionality (power) of this MeasureUnit. For example, if the unit is square,
+     * then 2 is returned.
+     *
+     * NOTE: Only works on SINGLE units. If this is a COMPOUND or SEQUENCE unit, an error will
+     * occur. For more information, see UMeasureUnitComplexity.
+     *
+     * @param status Set if this is not a SINGLE unit or if another error occurs.
+     * @return The dimensionality (power) of this simple unit.
+     * @draft ICU 67
+     */
+    int32_t getDimensionality(UErrorCode& status) const;
+
+    /**
+     * Gets the reciprocal of this MeasureUnit, with the numerator and denominator flipped.
+     *
+     * For example, if the receiver is "meter-per-second", the unit "second-per-meter" is returned.
+     *
+     * NOTE: Only works on SINGLE and COMPOUND units. If this is a SEQUENCE unit, an error will
+     * occur. For more information, see UMeasureUnitComplexity.
+     *
+     * @param status Set if this is a SEQUENCE unit or if another error occurs.
+     * @return The reciprocal of the target unit.
+     * @draft ICU 67
+     */
+    MeasureUnit reciprocal(UErrorCode& status) const;
+
+    /**
+     * Gets the product of this unit with another unit. This is a way to build units from
+     * constituent parts.
+     *
+     * The numerator and denominator are preserved through this operation.
+     *
+     * For example, if the receiver is "kilowatt" and the argument is "hour-per-day", then the
+     * unit "kilowatt-hour-per-day" is returned.
+     *
+     * NOTE: Only works on SINGLE and COMPOUND units. If either unit (receivee and argument) is a
+     * SEQUENCE unit, an error will occur. For more information, see UMeasureUnitComplexity.
+     *
+     * @param other The MeasureUnit to multiply with the target.
+     * @param status Set if this or other is a SEQUENCE unit or if another error occurs.
+     * @return The product of the target unit with the provided unit.
+     * @draft ICU 67
+     */
+    MeasureUnit product(const MeasureUnit& other, UErrorCode& status) const;
+#endif // U_HIDE_DRAFT_API
+
+#ifndef U_HIDE_INTERNAL_API
+    /**
+     * Gets the list of SINGLE units contained within a SEQUENCE of COMPOUND unit.
+     *
+     * Examples:
+     * - Given "meter-kilogram-per-second", three units will be returned: "meter",
+     *   "kilogram", and "one-per-second".
+     * - Given "hour+minute+second", three units will be returned: "hour", "minute",
+     *   and "second".
+     *
+     * If this is a SINGLE unit, an array of length 1 will be returned.
+     *
+     * TODO(ICU-21021): Finalize this API and propose it as draft.
+     *
+     * @param outCount The number of elements in the return array.
+     * @param status Set if an error occurs.
+     * @return An array of single units, owned by the caller.
+     * @internal ICU 67 Technical Preview
+     */
+    LocalArray<MeasureUnit> splitToSingleUnits(int32_t& outCount, UErrorCode& status) const;
+#endif // U_HIDE_INTERNAL_API
+
     /**
      * getAvailable gets all of the available units.
      * If there are too many units to fit into destCapacity then the
@@ -196,26 +559,6 @@
 
     /**
      * ICU use only.
-     * @return Whether subType is known to ICU.
-     * @internal
-     */
-    static bool findBySubType(StringPiece subType, MeasureUnit* output);
-
-    /**
-     * ICU use only.
-     * Parse a core unit identifier into a numerator and denominator unit.
-     * @param coreUnitIdentifier The string to parse.
-     * @param numerator Output: set to the numerator unit.
-     * @param denominator Output: set to the denominator unit, if present.
-     * @param status Set to U_ILLEGAL_ARGUMENT_ERROR if the core unit identifier is not known.
-     * @return Whether both a numerator and denominator are returned.
-     * @internal
-     */
-    static bool parseCoreUnitIdentifier(
-        StringPiece coreUnitIdentifier, MeasureUnit* numerator, MeasureUnit* denominator, UErrorCode& status);
-
-    /**
-     * ICU use only.
      * @internal
      */
     static MeasureUnit resolveUnitPerUnit(
@@ -3342,7 +3685,7 @@
      * For ICU use only.
      * @internal
      */
-    void initCurrency(const char *isoCurrency);
+    void initCurrency(StringPiece isoCurrency);
 
     /**
      * For ICU use only.
@@ -3353,16 +3696,26 @@
 #endif  /* U_HIDE_INTERNAL_API */
 
 private:
-    int32_t fTypeId;
-    int32_t fSubTypeId;
-    char fCurrency[4];
 
-    MeasureUnit(int32_t typeId, int32_t subTypeId) : fTypeId(typeId), fSubTypeId(subTypeId) {
-        fCurrency[0] = 0;
-    }
+    // If non-null, fImpl is owned by the MeasureUnit.
+    MeasureUnitImpl* fImpl;
+
+    // These two ints are indices into static string lists in measunit.cpp
+    int16_t fSubTypeId;
+    int8_t fTypeId;
+
+    MeasureUnit(int32_t typeId, int32_t subTypeId);
+    MeasureUnit(MeasureUnitImpl&& impl);
     void setTo(int32_t typeId, int32_t subTypeId);
     int32_t getOffset() const;
     static MeasureUnit *create(int typeId, int subTypeId, UErrorCode &status);
+
+    /**
+     * @return Whether subType is known to ICU.
+     */
+    static bool findBySubType(StringPiece subType, MeasureUnit* output);
+
+    friend struct MeasureUnitImpl;
 };
 
 U_NAMESPACE_END
diff --git a/icu4c/source/i18n/unicode/numberformatter.h b/icu4c/source/i18n/unicode/numberformatter.h
index 112a285..985c02d 100644
--- a/icu4c/source/i18n/unicode/numberformatter.h
+++ b/icu4c/source/i18n/unicode/numberformatter.h
@@ -1436,6 +1436,16 @@
 
 } // namespace impl
 
+#if (U_PF_WINDOWS <= U_PLATFORM && U_PLATFORM <= U_PF_CYGWIN) && defined(_MSC_VER)
+// Ignore MSVC warning 4661. This is generated for NumberFormatterSettings<>::toSkeleton() as this method
+// is defined elsewhere (in number_skeletons.cpp). The compiler is warning that the explicit template instantiation
+// inside this single translation unit (CPP file) is incomplete, and thus it isn't sure if the template class is
+// fully defined. However, since each translation unit explicitly instantiates all the necessary template classes,
+// they will all be passed to the linker, and the linker will still find and export all the class members.
+#pragma warning(push)
+#pragma warning(disable: 4661)
+#endif
+
 /**
  * An abstract base class for specifying settings related to number formatting. This class is implemented by
  * {@link UnlocalizedNumberFormatter} and {@link LocalizedNumberFormatter}. This class is not intended for
@@ -2402,6 +2412,11 @@
     friend class UnlocalizedNumberFormatter;
 };
 
+#if (U_PF_WINDOWS <= U_PLATFORM && U_PLATFORM <= U_PF_CYGWIN) && defined(_MSC_VER)
+// Warning 4661.
+#pragma warning(pop)
+#endif
+
 /**
  * The result of a number formatting operation. This class allows the result to be exported in several data types,
  * including a UnicodeString and a FieldPositionIterator.
diff --git a/icu4c/source/test/depstest/dependencies.txt b/icu4c/source/test/depstest/dependencies.txt
index 8437b4e..e096586 100644
--- a/icu4c/source/test/depstest/dependencies.txt
+++ b/icu4c/source/test/depstest/dependencies.txt
@@ -869,7 +869,8 @@
     dayperiodrules
     listformatter
     formatting formattable_cnv regex regex_cnv translit
-    double_conversion number_representation number_output numberformatter numberparser
+    double_conversion number_representation number_output numberformatter number_skeletons numberparser
+    units_extra
     universal_time_scale
     uclean_i18n
 
@@ -981,15 +982,15 @@
 
 group: numberformatter
     # ICU 60+ NumberFormatter API
-    number_affixutils.o number_asformat.o
-    number_capi.o number_compact.o number_currencysymbols.o
+    number_affixutils.o
+    number_compact.o number_currencysymbols.o
     number_decimfmtprops.o
     number_fluent.o number_formatimpl.o
     number_grouping.o number_integerwidth.o number_longnames.o
     number_mapper.o number_modifiers.o number_multiplier.o
     number_notation.o number_padding.o
     number_patternmodifier.o number_patternstring.o number_rounding.o
-    number_scientific.o number_skeletons.o
+    number_scientific.o
     currpinf.o dcfmtsym.o numsys.o
     numrange_fluent.o numrange_impl.o
   deps
@@ -997,6 +998,13 @@
     number_representation number_output
     uclean_i18n common
 
+group: number_skeletons
+    # Number skeleton support; separated from numberformatter
+    number_skeletons.o number_capi.o number_asformat.o
+  deps
+    numberformatter
+    units_extra
+
 group: numberparser
     numparse_affixes.o numparse_compositions.o numparse_currency.o
     numparse_decimal.o numparse_impl.o numparse_parsednumber.o
@@ -1037,7 +1045,8 @@
     # messageformat
     choicfmt.o msgfmt.o plurfmt.o selfmt.o umsg.o
   deps
-    decnumber formattable format units numberformatter numberparser formatted_value_sbimpl
+    decnumber formattable format units numberformatter number_skeletons numberparser
+    formatted_value_sbimpl
     listformatter
     dayperiodrules
     collation collation_builder  # for rbnf
@@ -1053,10 +1062,15 @@
   deps
     breakiterator
 
+group: units_extra
+    measunit_extra.o
+  deps
+    units ucharstriebuilder ucharstrie uclean_i18n
+
 group: units
     measunit.o currunit.o nounit.o
   deps
-    stringenumeration
+    stringenumeration errorcode
 
 group: decnumber
     decContext.o decNumber.o
diff --git a/icu4c/source/test/intltest/measfmttest.cpp b/icu4c/source/test/intltest/measfmttest.cpp
index 2b53f8b..4846540 100644
--- a/icu4c/source/test/intltest/measfmttest.cpp
+++ b/icu4c/source/test/intltest/measfmttest.cpp
@@ -79,6 +79,10 @@
     void Test20332_PersonUnits();
     void TestNumericTime();
     void TestNumericTimeSomeSpecialFormats();
+    void TestInvalidIdentifiers();
+    void TestCompoundUnitOperations();
+    void TestIdentifiers();
+
     void verifyFormat(
         const char *description,
         const MeasureFormat &fmt,
@@ -138,6 +142,21 @@
         NumberFormat::EAlignmentFields field,
         int32_t start,
         int32_t end);
+    void verifySingleUnit(
+        const MeasureUnit& unit,
+        UMeasureSIPrefix siPrefix,
+        int8_t power,
+        const char* identifier);
+    void verifyCompoundUnit(
+        const MeasureUnit& unit,
+        const char* identifier,
+        const char** subIdentifiers,
+        int32_t subIdentifierCount);
+    void verifySequenceUnit(
+        const MeasureUnit& unit,
+        const char* identifier,
+        const char** subIdentifiers,
+        int32_t subIdentifierCount);
 };
 
 void MeasureFormatTest::runIndexedTest(
@@ -182,6 +201,9 @@
     TESTCASE_AUTO(Test20332_PersonUnits);
     TESTCASE_AUTO(TestNumericTime);
     TESTCASE_AUTO(TestNumericTimeSomeSpecialFormats);
+    TESTCASE_AUTO(TestInvalidIdentifiers);
+    TESTCASE_AUTO(TestCompoundUnitOperations);
+    TESTCASE_AUTO(TestIdentifiers);
     TESTCASE_AUTO_END;
 }
 
@@ -3215,6 +3237,212 @@
     verifyFormat("Danish fhoursFminutes", fmtDa, fhoursFminutes, 2, "2.03,877");
 }
 
+void MeasureFormatTest::TestInvalidIdentifiers() {
+    IcuTestErrorCode status(*this, "TestInvalidIdentifiers");
+
+    const char* const inputs[] = {
+        "kilo",
+        "kilokilo",
+        "onekilo",
+        "meterkilo",
+        "meter-kilo",
+        "k",
+        "meter-",
+        "meter+",
+        "-meter",
+        "+meter",
+        "-kilometer",
+        "+kilometer",
+        "-p2-meter",
+        "+p2-meter",
+        "+",
+        "-"
+    };
+
+    for (const auto& input : inputs) {
+        status.setScope(input);
+        MeasureUnit::forIdentifier(input, status);
+        status.expectErrorAndReset(U_ILLEGAL_ARGUMENT_ERROR);
+    }
+}
+
+void MeasureFormatTest::TestCompoundUnitOperations() {
+    IcuTestErrorCode status(*this, "TestCompoundUnitOperations");
+
+    MeasureUnit::forIdentifier("kilometer-per-second-joule", status);
+
+    MeasureUnit kilometer = MeasureUnit::getKilometer();
+    MeasureUnit cubicMeter = MeasureUnit::getCubicMeter();
+    MeasureUnit meter = kilometer.withSIPrefix(UMEASURE_SI_PREFIX_ONE, status);
+    MeasureUnit centimeter1 = kilometer.withSIPrefix(UMEASURE_SI_PREFIX_CENTI, status);
+    MeasureUnit centimeter2 = meter.withSIPrefix(UMEASURE_SI_PREFIX_CENTI, status);
+    MeasureUnit cubicDecimeter = cubicMeter.withSIPrefix(UMEASURE_SI_PREFIX_DECI, status);
+
+    verifySingleUnit(kilometer, UMEASURE_SI_PREFIX_KILO, 1, "kilometer");
+    verifySingleUnit(meter, UMEASURE_SI_PREFIX_ONE, 1, "meter");
+    verifySingleUnit(centimeter1, UMEASURE_SI_PREFIX_CENTI, 1, "centimeter");
+    verifySingleUnit(centimeter2, UMEASURE_SI_PREFIX_CENTI, 1, "centimeter");
+    verifySingleUnit(cubicDecimeter, UMEASURE_SI_PREFIX_DECI, 3, "cubic-decimeter");
+
+    assertTrue("centimeter equality", centimeter1 == centimeter2);
+    assertTrue("kilometer inequality", centimeter1 != kilometer);
+
+    MeasureUnit squareMeter = meter.withDimensionality(2, status);
+    MeasureUnit overCubicCentimeter = centimeter1.withDimensionality(-3, status);
+    MeasureUnit quarticKilometer = kilometer.withDimensionality(4, status);
+    MeasureUnit overQuarticKilometer1 = kilometer.withDimensionality(-4, status);
+
+    verifySingleUnit(squareMeter, UMEASURE_SI_PREFIX_ONE, 2, "square-meter");
+    verifySingleUnit(overCubicCentimeter, UMEASURE_SI_PREFIX_CENTI, -3, "one-per-cubic-centimeter");
+    verifySingleUnit(quarticKilometer, UMEASURE_SI_PREFIX_KILO, 4, "p4-kilometer");
+    verifySingleUnit(overQuarticKilometer1, UMEASURE_SI_PREFIX_KILO, -4, "one-per-p4-kilometer");
+
+    assertTrue("power inequality", quarticKilometer != overQuarticKilometer1);
+
+    MeasureUnit overQuarticKilometer2 = quarticKilometer.reciprocal(status);
+    MeasureUnit overQuarticKilometer3 = kilometer.product(kilometer, status)
+        .product(kilometer, status)
+        .product(kilometer, status)
+        .reciprocal(status);
+    MeasureUnit overQuarticKilometer4 = meter.withDimensionality(4, status)
+        .reciprocal(status)
+        .withSIPrefix(UMEASURE_SI_PREFIX_KILO, status);
+
+    verifySingleUnit(overQuarticKilometer2, UMEASURE_SI_PREFIX_KILO, -4, "one-per-p4-kilometer");
+    verifySingleUnit(overQuarticKilometer3, UMEASURE_SI_PREFIX_KILO, -4, "one-per-p4-kilometer");
+    verifySingleUnit(overQuarticKilometer4, UMEASURE_SI_PREFIX_KILO, -4, "one-per-p4-kilometer");
+
+    assertTrue("reciprocal equality", overQuarticKilometer1 == overQuarticKilometer2);
+    assertTrue("reciprocal equality", overQuarticKilometer1 == overQuarticKilometer3);
+    assertTrue("reciprocal equality", overQuarticKilometer1 == overQuarticKilometer4);
+
+    MeasureUnit kiloSquareSecond = MeasureUnit::getSecond()
+        .withDimensionality(2, status).withSIPrefix(UMEASURE_SI_PREFIX_KILO, status);
+    MeasureUnit meterSecond = meter.product(kiloSquareSecond, status);
+    MeasureUnit cubicMeterSecond1 = meter.withDimensionality(3, status).product(kiloSquareSecond, status);
+    MeasureUnit centimeterSecond1 = meter.withSIPrefix(UMEASURE_SI_PREFIX_CENTI, status).product(kiloSquareSecond, status);
+    MeasureUnit secondCubicMeter = kiloSquareSecond.product(meter.withDimensionality(3, status), status);
+    MeasureUnit secondCentimeter = kiloSquareSecond.product(meter.withSIPrefix(UMEASURE_SI_PREFIX_CENTI, status), status);
+    MeasureUnit secondCentimeterPerKilometer = secondCentimeter.product(kilometer.reciprocal(status), status);
+
+    verifySingleUnit(kiloSquareSecond, UMEASURE_SI_PREFIX_KILO, 2, "square-kilosecond");
+    const char* meterSecondSub[] = {"meter", "square-kilosecond"};
+    verifyCompoundUnit(meterSecond, "meter-square-kilosecond",
+        meterSecondSub, UPRV_LENGTHOF(meterSecondSub));
+    const char* cubicMeterSecond1Sub[] = {"cubic-meter", "square-kilosecond"};
+    verifyCompoundUnit(cubicMeterSecond1, "cubic-meter-square-kilosecond",
+        cubicMeterSecond1Sub, UPRV_LENGTHOF(cubicMeterSecond1Sub));
+    const char* centimeterSecond1Sub[] = {"centimeter", "square-kilosecond"};
+    verifyCompoundUnit(centimeterSecond1, "centimeter-square-kilosecond",
+        centimeterSecond1Sub, UPRV_LENGTHOF(centimeterSecond1Sub));
+    const char* secondCubicMeterSub[] = {"cubic-meter", "square-kilosecond"};
+    verifyCompoundUnit(secondCubicMeter, "cubic-meter-square-kilosecond",
+        secondCubicMeterSub, UPRV_LENGTHOF(secondCubicMeterSub));
+    const char* secondCentimeterSub[] = {"centimeter", "square-kilosecond"};
+    verifyCompoundUnit(secondCentimeter, "centimeter-square-kilosecond",
+        secondCentimeterSub, UPRV_LENGTHOF(secondCentimeterSub));
+    const char* secondCentimeterPerKilometerSub[] = {"centimeter", "square-kilosecond", "one-per-kilometer"};
+    verifyCompoundUnit(secondCentimeterPerKilometer, "centimeter-square-kilosecond-per-kilometer",
+        secondCentimeterPerKilometerSub, UPRV_LENGTHOF(secondCentimeterPerKilometerSub));
+
+    assertTrue("reordering equality", cubicMeterSecond1 == secondCubicMeter);
+    assertTrue("additional simple units inequality", secondCubicMeter != secondCentimeter);
+
+    // Don't allow get/set power or SI prefix on compound units
+    status.errIfFailureAndReset();
+    meterSecond.getDimensionality(status);
+    status.expectErrorAndReset(U_ILLEGAL_ARGUMENT_ERROR);
+    meterSecond.withDimensionality(3, status);
+    status.expectErrorAndReset(U_ILLEGAL_ARGUMENT_ERROR);
+    meterSecond.getSIPrefix(status);
+    status.expectErrorAndReset(U_ILLEGAL_ARGUMENT_ERROR);
+    meterSecond.withSIPrefix(UMEASURE_SI_PREFIX_CENTI, status);
+    status.expectErrorAndReset(U_ILLEGAL_ARGUMENT_ERROR);
+
+    // Test that StringPiece does not overflow
+    MeasureUnit centimeter3 = MeasureUnit::forIdentifier({secondCentimeter.getIdentifier(), 10}, status);
+    verifySingleUnit(centimeter3, UMEASURE_SI_PREFIX_CENTI, 1, "centimeter");
+    assertTrue("string piece equality", centimeter1 == centimeter3);
+
+    MeasureUnit footInch = MeasureUnit::forIdentifier("foot-and-inch", status);
+    MeasureUnit inchFoot = MeasureUnit::forIdentifier("inch-and-foot", status);
+
+    const char* footInchSub[] = {"foot", "inch"};
+    verifySequenceUnit(footInch, "foot-and-inch",
+        footInchSub, UPRV_LENGTHOF(footInchSub));
+    const char* inchFootSub[] = {"inch", "foot"};
+    verifySequenceUnit(inchFoot, "inch-and-foot",
+        inchFootSub, UPRV_LENGTHOF(inchFootSub));
+
+    assertTrue("order matters inequality", footInch != inchFoot);
+
+    MeasureUnit one1;
+    MeasureUnit one2 = MeasureUnit::forIdentifier("one", status);
+    MeasureUnit one3 = MeasureUnit::forIdentifier("", status);
+    MeasureUnit squareOne = one2.withDimensionality(2, status);
+    MeasureUnit onePerOne = one2.reciprocal(status);
+    MeasureUnit squareKiloOne = squareOne.withSIPrefix(UMEASURE_SI_PREFIX_KILO, status);
+    MeasureUnit onePerSquareKiloOne = squareKiloOne.reciprocal(status);
+    MeasureUnit oneOne = MeasureUnit::forIdentifier("one-one", status);
+    MeasureUnit onePlusOne = MeasureUnit::forIdentifier("one-and-one", status);
+    MeasureUnit kilometer2 = one2.product(kilometer, status);
+
+    verifySingleUnit(one1, UMEASURE_SI_PREFIX_ONE, 1, "one");
+    verifySingleUnit(one2, UMEASURE_SI_PREFIX_ONE, 1, "one");
+    verifySingleUnit(one3, UMEASURE_SI_PREFIX_ONE, 1, "one");
+    verifySingleUnit(squareOne, UMEASURE_SI_PREFIX_ONE, 1, "one");
+    verifySingleUnit(onePerOne, UMEASURE_SI_PREFIX_ONE, 1, "one");
+    verifySingleUnit(squareKiloOne, UMEASURE_SI_PREFIX_ONE, 1, "one");
+    verifySingleUnit(onePerSquareKiloOne, UMEASURE_SI_PREFIX_ONE, 1, "one");
+    verifySingleUnit(oneOne, UMEASURE_SI_PREFIX_ONE, 1, "one");
+    verifySingleUnit(onePlusOne, UMEASURE_SI_PREFIX_ONE, 1, "one");
+    verifySingleUnit(kilometer2, UMEASURE_SI_PREFIX_KILO, 1, "kilometer");
+
+    assertTrue("one equality", one1 == one2);
+    assertTrue("one equality", one2 == one3);
+    assertTrue("one-per-one equality", onePerOne == onePerSquareKiloOne);
+    assertTrue("kilometer equality", kilometer == kilometer2);
+
+    // Test out-of-range powers
+    MeasureUnit power15 = MeasureUnit::forIdentifier("p15-kilometer", status);
+    verifySingleUnit(power15, UMEASURE_SI_PREFIX_KILO, 15, "p15-kilometer");
+    status.errIfFailureAndReset();
+    MeasureUnit power16a = MeasureUnit::forIdentifier("p16-kilometer", status);
+    status.expectErrorAndReset(U_ILLEGAL_ARGUMENT_ERROR);
+    MeasureUnit power16b = power15.product(kilometer, status);
+    status.expectErrorAndReset(U_ILLEGAL_ARGUMENT_ERROR);
+    MeasureUnit powerN15 = MeasureUnit::forIdentifier("one-per-p15-kilometer", status);
+    verifySingleUnit(powerN15, UMEASURE_SI_PREFIX_KILO, -15, "one-per-p15-kilometer");
+    status.errIfFailureAndReset();
+    MeasureUnit powerN16a = MeasureUnit::forIdentifier("one-per-p16-kilometer", status);
+    status.expectErrorAndReset(U_ILLEGAL_ARGUMENT_ERROR);
+    MeasureUnit powerN16b = powerN15.product(overQuarticKilometer1, status);
+    status.expectErrorAndReset(U_ILLEGAL_ARGUMENT_ERROR);
+}
+
+void MeasureFormatTest::TestIdentifiers() {
+    IcuTestErrorCode status(*this, "TestIdentifiers");
+    struct TestCase {
+        bool valid;
+        const char* id;
+        const char* normalized;
+    } cases[] = {
+        { true, "square-meter-per-square-meter", "square-meter-per-square-meter" },
+        // TODO(ICU-20920): Add more test cases once the proper ranking is available.
+    };
+    for (const auto& cas : cases) {
+        status.setScope(cas.id);
+        MeasureUnit unit = MeasureUnit::forIdentifier(cas.id, status);
+        if (!cas.valid) {
+            status.expectErrorAndReset(U_ILLEGAL_ARGUMENT_ERROR);
+            continue;
+        }
+        const char* actual = unit.getIdentifier();
+        assertEquals(cas.id, cas.normalized, actual);
+        status.errIfFailureAndReset();
+    }
+}
+
 
 void MeasureFormatTest::verifyFieldPosition(
         const char *description,
@@ -3286,6 +3514,97 @@
     }
 }
 
+void MeasureFormatTest::verifySingleUnit(
+        const MeasureUnit& unit,
+        UMeasureSIPrefix siPrefix,
+        int8_t power,
+        const char* identifier) {
+    IcuTestErrorCode status(*this, "verifySingleUnit");
+    UnicodeString uid(identifier, -1, US_INV);
+    assertEquals(uid + ": SI prefix",
+        siPrefix,
+        unit.getSIPrefix(status));
+    status.errIfFailureAndReset("%s: SI prefix", identifier);
+    assertEquals(uid + ": Power",
+        static_cast<int32_t>(power),
+        static_cast<int32_t>(unit.getDimensionality(status)));
+    status.errIfFailureAndReset("%s: Power", identifier);
+    assertEquals(uid + ": Identifier",
+        identifier,
+        unit.getIdentifier());
+    status.errIfFailureAndReset("%s: Identifier", identifier);
+    assertTrue(uid + ": Constructor",
+        unit == MeasureUnit::forIdentifier(identifier, status));
+    status.errIfFailureAndReset("%s: Constructor", identifier);
+    assertEquals(uid + ": Complexity",
+        UMEASURE_UNIT_SINGLE,
+        unit.getComplexity(status));
+    status.errIfFailureAndReset("%s: Complexity", identifier);
+}
+
+void MeasureFormatTest::verifyCompoundUnit(
+        const MeasureUnit& unit,
+        const char* identifier,
+        const char** subIdentifiers,
+        int32_t subIdentifierCount) {
+    IcuTestErrorCode status(*this, "verifyCompoundUnit");
+    UnicodeString uid(identifier, -1, US_INV);
+    assertEquals(uid + ": Identifier",
+        identifier,
+        unit.getIdentifier());
+    status.errIfFailureAndReset("%s: Identifier", identifier);
+    assertTrue(uid + ": Constructor",
+        unit == MeasureUnit::forIdentifier(identifier, status));
+    status.errIfFailureAndReset("%s: Constructor", identifier);
+    assertEquals(uid + ": Complexity",
+        UMEASURE_UNIT_COMPOUND,
+        unit.getComplexity(status));
+    status.errIfFailureAndReset("%s: Complexity", identifier);
+
+    int32_t length;
+    LocalArray<MeasureUnit> subUnits = unit.splitToSingleUnits(length, status);
+    assertEquals(uid + ": Length", subIdentifierCount, length);
+    for (int32_t i = 0;; i++) {
+        if (i >= subIdentifierCount || i >= length) break;
+        assertEquals(uid + ": Sub-unit #" + Int64ToUnicodeString(i),
+            subIdentifiers[i],
+            subUnits[i].getIdentifier());
+        assertEquals(uid + ": Sub-unit Complexity",
+            UMEASURE_UNIT_SINGLE,
+            subUnits[i].getComplexity(status));
+    }
+}
+
+void MeasureFormatTest::verifySequenceUnit(
+        const MeasureUnit& unit,
+        const char* identifier,
+        const char** subIdentifiers,
+        int32_t subIdentifierCount) {
+    IcuTestErrorCode status(*this, "verifySequenceUnit");
+    UnicodeString uid(identifier, -1, US_INV);
+    assertEquals(uid + ": Identifier",
+        identifier,
+        unit.getIdentifier());
+    status.errIfFailureAndReset("%s: Identifier", identifier);
+    assertTrue(uid + ": Constructor",
+        unit == MeasureUnit::forIdentifier(identifier, status));
+    status.errIfFailureAndReset("%s: Constructor", identifier);
+    assertEquals(uid + ": Complexity",
+        UMEASURE_UNIT_SEQUENCE,
+        unit.getComplexity(status));
+    status.errIfFailureAndReset("%s: Complexity", identifier);
+
+    int32_t length;
+    LocalArray<MeasureUnit> subUnits = unit.splitToSingleUnits(length, status);
+    assertEquals(uid + ": Length", subIdentifierCount, length);
+    for (int32_t i = 0;; i++) {
+        if (i >= subIdentifierCount || i >= length) break;
+        assertEquals(uid + ": Sub-unit #" + Int64ToUnicodeString(i),
+            subIdentifiers[i],
+            subUnits[i].getIdentifier());
+    }
+}
+
 extern IntlTest *createMeasureFormatTest() {
     return new MeasureFormatTest();
 }
diff --git a/icu4c/source/test/intltest/numbertest_api.cpp b/icu4c/source/test/intltest/numbertest_api.cpp
index 01494ff..60f4d44 100644
--- a/icu4c/source/test/intltest/numbertest_api.cpp
+++ b/icu4c/source/test/intltest/numbertest_api.cpp
@@ -675,7 +675,7 @@
     assertFormatDescending(
             u"Meters Per Second Short (unit that simplifies) and perUnit method",
             u"measure-unit/length-meter per-measure-unit/duration-second",
-            u"~unit/meter-per-second", // does not round-trip to the full skeleton above
+            u"unit/meter-per-second",
             NumberFormatter::with().unit(METER).perUnit(SECOND),
             Locale::getEnglish(),
             u"87,650 m/s",
@@ -719,6 +719,23 @@
             u"0.08765 J/fur",
             u"0.008765 J/fur",
             u"0 J/fur");
+
+    // TODO(ICU-20941): Support constructions such as this one.
+    // assertFormatDescending(
+    //         u"Joules Per Furlong Short with unit identifier via API",
+    //         u"measure-unit/energy-joule per-measure-unit/length-furlong",
+    //         u"unit/joule-per-furlong",
+    //         NumberFormatter::with().unit(MeasureUnit::forIdentifier("joule-per-furlong", status)),
+    //         Locale::getEnglish(),
+    //         u"87,650 J/fur",
+    //         u"8,765 J/fur",
+    //         u"876.5 J/fur",
+    //         u"87.65 J/fur",
+    //         u"8.765 J/fur",
+    //         u"0.8765 J/fur",
+    //         u"0.08765 J/fur",
+    //         u"0.008765 J/fur",
+    //         u"0 J/fur");
 }
 
 void NumberFormatterApiTest::unitCurrency() {
@@ -2811,7 +2828,7 @@
         FormattedNumber result = assertFormatSingle(
                 message,
                 u"measure-unit/length-meter per-measure-unit/duration-second unit-width-full-name",
-                u"~unit/meter-per-second unit-width-full-name", // does not round-trip to the full skeleton above
+                u"unit/meter-per-second unit-width-full-name",
                 NumberFormatter::with().unit(METER).perUnit(SECOND).unitWidth(UNUM_UNIT_WIDTH_FULL_NAME),
                 "ky", // locale with the interesting data
                 68,
diff --git a/icu4c/source/test/intltest/numfmtst.cpp b/icu4c/source/test/intltest/numfmtst.cpp
index 9ebd26e..316a743 100644
--- a/icu4c/source/test/intltest/numfmtst.cpp
+++ b/icu4c/source/test/intltest/numfmtst.cpp
@@ -2166,6 +2166,8 @@
     static const UChar BAD2[] = u"??A";
     static const UChar XXX[]  = u"XXX";
     static const char XXX8[]  =  "XXX";
+    static const UChar XYZ[]  = u"XYZ";
+    static const char XYZ8[]  =  "XYZ";
     static const UChar INV[]  = u"{$%";
     static const char INV8[]  =  "{$%";
     static const UChar ZZZ[]  = u"zz";
@@ -2182,10 +2184,16 @@
 
     CurrencyUnit cu(USD, ec);
     assertSuccess("CurrencyUnit", ec);
-
     assertEquals("getISOCurrency()", USD, cu.getISOCurrency());
     assertEquals("getSubtype()", USD8, cu.getSubtype());
 
+    // Test XYZ, a valid but non-standard currency.
+    // Note: Country code XY is private-use, so XYZ should remain unallocated.
+    CurrencyUnit extended(XYZ, ec);
+    assertSuccess("non-standard", ec);
+    assertEquals("non-standard", XYZ, extended.getISOCurrency());
+    assertEquals("non-standard", XYZ8, extended.getSubtype());
+
     CurrencyUnit inv(INV, ec);
     assertEquals("non-invariant", U_INVARIANT_CONVERSION_ERROR, ec);
     assertEquals("non-invariant", XXX, inv.getISOCurrency());
@@ -2259,15 +2267,20 @@
     // Test slicing
     MeasureUnit sliced1 = cu;
     MeasureUnit sliced2 = cu;
+    MeasureUnit sliced3 = extended;
     assertEquals("Subtype after slicing 1", USD8, sliced1.getSubtype());
     assertEquals("Subtype after slicing 2", USD8, sliced2.getSubtype());
+    assertEquals("Subtype after slicing 3", XYZ8, sliced3.getSubtype());
     CurrencyUnit restored1(sliced1, ec);
     CurrencyUnit restored2(sliced2, ec);
+    CurrencyUnit restored3(sliced3, ec);
     assertSuccess("Restoring from MeasureUnit", ec);
     assertEquals("Subtype after restoring 1", USD8, restored1.getSubtype());
     assertEquals("Subtype after restoring 2", USD8, restored2.getSubtype());
+    assertEquals("Subtype after restoring 3", XYZ8, restored3.getSubtype());
     assertEquals("ISO Code after restoring 1", USD, restored1.getISOCurrency());
     assertEquals("ISO Code after restoring 2", USD, restored2.getISOCurrency());
+    assertEquals("ISO Code after restoring 3", XYZ, restored3.getISOCurrency());
 
     // Test copy constructor failure
     LocalPointer<MeasureUnit> meter(MeasureUnit::createMeter(ec));