diff --git a/clang/lib/ExtractAPI/Serialization/ranges_transform.module.verify.cpp b/clang/lib/ExtractAPI/Serialization/ranges_transform.module.verify.cpp
new file mode 100644
--- /dev/null
+++ b/clang/lib/ExtractAPI/Serialization/ranges_transform.module.verify.cpp
@@ -0,0 +1,15 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: modules-build
+
+// WARNING: This test was generated by 'generate_private_header_tests.py'
+// and should not be edited manually.
+
+// expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_transform.h'}}
+#include <__algorithm/ranges_transform.h>
diff --git a/libcxx/docs/Status/RangesAlgorithms.csv b/libcxx/docs/Status/RangesAlgorithms.csv
--- a/libcxx/docs/Status/RangesAlgorithms.csv
+++ b/libcxx/docs/Status/RangesAlgorithms.csv
@@ -44,7 +44,7 @@
 Write,move_backward,Not assigned,n/a,Not started
 Write,fill,Not assigned,n/a,Not started
 Write,fill_n,Not assigned,n/a,Not started
-Write,transform,Not assigned,n/a,Not started
+Write,transform,Nikolas Klauser,`D122173 <https://llvm.org/D122173>`_,✅
 Write,generate,Not assigned,n/a,Not started
 Write,generate_n,Not assigned,n/a,Not started
 Write,remove_copy,Not assigned,n/a,Not started
diff --git a/libcxx/include/CMakeLists.txt b/libcxx/include/CMakeLists.txt
--- a/libcxx/include/CMakeLists.txt
+++ b/libcxx/include/CMakeLists.txt
@@ -75,6 +75,7 @@
   __algorithm/ranges_min_element.h
   __algorithm/ranges_mismatch.h
   __algorithm/ranges_swap_ranges.h
+  __algorithm/ranges_transform.h
   __algorithm/remove.h
   __algorithm/remove_copy.h
   __algorithm/remove_copy_if.h
diff --git a/libcxx/include/__algorithm/ranges_transform.h b/libcxx/include/__algorithm/ranges_transform.h
new file mode 100644
--- /dev/null
+++ b/libcxx/include/__algorithm/ranges_transform.h
@@ -0,0 +1,170 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___ALGORITHM_RANGES_TRANSFORM_H
+#define _LIBCPP___ALGORITHM_RANGES_TRANSFORM_H
+
+#include <__algorithm/in_in_out_result.h>
+#include <__algorithm/in_out_result.h>
+#include <__concepts/constructible.h>
+#include <__config>
+#include <__functional/identity.h>
+#include <__functional/invoke.h>
+#include <__iterator/concepts.h>
+#include <__iterator/projected.h>
+#include <__ranges/access.h>
+#include <__ranges/concepts.h>
+#include <__ranges/dangling.h>
+#include <__utility/move.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_INCOMPLETE_RANGES)
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+namespace ranges {
+
+template <class _Ip, class _Op>
+using unary_transform_result = in_out_result<_Ip, _Op>;
+
+template <class _I1, class _I2, class _O1>
+using binary_transform_result = in_in_out_result<_I1, _I2, _O1>;
+
+namespace __transform {
+struct __fn {
+private:
+  template <class _InIter, class _Sent,
+            class _OutIter,
+            class _Func,
+            class _Proj>
+  _LIBCPP_HIDE_FROM_ABI static constexpr
+  unary_transform_result<_InIter, _OutIter> __unary(_InIter __first, _Sent __last,
+                                                    _OutIter __result,
+                                                    _Func& __operation,
+                                                    _Proj& __projection) {
+    while (__first != __last) {
+      *__result = std::invoke(__operation, std::invoke(__projection, *__first));
+      ++__first;
+      ++__result;
+    }
+
+    return {std::move(__first), std::move(__result)};
+  }
+
+  template <class _InIter1, class _Sent1,
+            class _InIter2, class _Sent2,
+            class _OutIter,
+            class _Func,
+            class _Proj1,
+            class _Proj2>
+  _LIBCPP_HIDE_FROM_ABI static constexpr binary_transform_result<_InIter1, _InIter2, _OutIter>
+  __binary(_InIter1 __first1, _Sent1 __last1,
+           _InIter2 __first2, _Sent2 __last2,
+           _OutIter __result,
+           _Func& __binary_operation,
+           _Proj1& __projection1,
+           _Proj2& __projection2) {
+    while (__first1 != __last1 && __first2 != __last2) {
+      *__result = std::invoke(__binary_operation, std::invoke(__projection1, *__first1),
+                                                  std::invoke(__projection2, *__first2));
+      ++__first1;
+      ++__first2;
+      ++__result;
+    }
+    return {std::move(__first1), std::move(__first2), std::move(__result)};
+  }
+public:
+  template <input_iterator _InIter, sentinel_for<_InIter> _Sent,
+            weakly_incrementable _OutIter,
+            copy_constructible _Func,
+            class _Proj = identity>
+    requires indirectly_writable<_OutIter, indirect_result_t<_Func&, projected<_InIter, _Proj>>>
+  _LIBCPP_HIDE_FROM_ABI constexpr
+  unary_transform_result<_InIter, _OutIter> operator()(_InIter __first, _Sent __last,
+                                                       _OutIter __result,
+                                                       _Func __operation,
+                                                       _Proj __proj = {}) const {
+    return __unary(std::move(__first), std::move(__last), std::move(__result), __operation, __proj);
+  }
+
+  template <input_range _Range,
+            weakly_incrementable _OutIter,
+            copy_constructible _Func,
+            class _Proj = identity>
+    requires indirectly_writable<_OutIter, indirect_result_t<_Func, projected<iterator_t<_Range>, _Proj>>>
+  _LIBCPP_HIDE_FROM_ABI constexpr
+  unary_transform_result<borrowed_iterator_t<_Range>, _OutIter> operator()(_Range&& __range,
+                                                                           _OutIter __result,
+                                                                           _Func __operation,
+                                                                           _Proj __projection = {}) const {
+    return __unary(ranges::begin(__range), ranges::end(__range), std::move(__result), __operation, __projection);
+  }
+
+  template <input_iterator _InIter1, sentinel_for<_InIter1> _Sent1,
+            input_iterator _InIter2, sentinel_for<_InIter2> _Sent2,
+            weakly_incrementable _OutIter,
+            copy_constructible _Func,
+            class _Proj1 = identity,
+            class _Proj2 = identity>
+    requires indirectly_writable<_OutIter, indirect_result_t<_Func&, projected<_InIter1, _Proj1>,
+                                                                     projected<_InIter2, _Proj2>>>
+  _LIBCPP_HIDE_FROM_ABI constexpr
+  binary_transform_result<_InIter1, _InIter2, _OutIter> operator()(_InIter1 __first1, _Sent1 __last1,
+                                                                   _InIter2 __first2, _Sent2 __last2,
+                                                                   _OutIter __result,
+                                                                   _Func __binary_operation,
+                                                                   _Proj1 __projection1 = {},
+                                                                   _Proj2 __projection2 = {}) const {
+    return __binary(std::move(__first1), std::move(__last1),
+                    std::move(__first2), std::move(__last2),
+                    std::move(__result),
+                    __binary_operation,
+                    __projection1,
+                    __projection2);
+  }
+
+  template <input_range _Range1,
+            input_range _Range2,
+            weakly_incrementable _OutIter,
+            copy_constructible _Func,
+            class _Proj1 = identity,
+            class _Proj2 = identity>
+    requires indirectly_writable<_OutIter, indirect_result_t<_Func&, projected<iterator_t<_Range1>, _Proj1>,
+                                                                     projected<iterator_t<_Range2>, _Proj2>>>
+  _LIBCPP_HIDE_FROM_ABI constexpr
+  binary_transform_result<borrowed_iterator_t<_Range1>, borrowed_iterator_t<_Range2>, _OutIter>
+  operator()(_Range1&& __range1,
+             _Range2&& __range2,
+             _OutIter __result,
+             _Func __binary_operation,
+             _Proj1 __projection1 = {},
+             _Proj2 __projection2 = {}) const {
+    return __binary(ranges::begin(__range1), ranges::end(__range1),
+                    ranges::begin(__range2), ranges::end(__range2),
+                    std::move(__result),
+                    __binary_operation,
+                    __projection1,
+                    __projection2);
+  }
+
+};
+} // namespace __transform
+
+inline namespace __cpo {
+  inline constexpr auto transform = __transform::__fn{};
+} // namespace __cpo
+} // namespace ranges
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_INCOMPLETE_RANGES)
+
+#endif // _LIBCPP___ALGORITHM_RANGES_TRANSFORM_H
diff --git a/libcxx/include/algorithm b/libcxx/include/algorithm
--- a/libcxx/include/algorithm
+++ b/libcxx/include/algorithm
@@ -110,6 +110,41 @@
     requires indirectly_copyable_storable<iterator_t<R>, range_value_t<R>*>
     constexpr range_value_t<R>
       max(R&& r, Comp comp = {}, Proj proj = {});                                   // since C++20
+
+  template<class I, class O>
+    using unary_transform_result = in_out_result<I, O>;                             // since C++20
+
+  template<class I1, class I2, class O>
+    using binary_transform_result = in_in_out_result<I1, I2, O>;                    // since C++20
+
+  template<input_iterator I, sentinel_for<I> S, weakly_incrementable O,
+           copy_constructible F, class Proj = identity>
+    requires indirectly_writable<O, indirect_result_t<F&, projected<I, Proj>>>
+    constexpr ranges::unary_transform_result<I, O>
+      transform(I first1, S last1, O result, F op, Proj proj = {});                 // since C++20
+
+  template<input_range R, weakly_incrementable O, copy_constructible F,
+           class Proj = identity>
+    requires indirectly_writable<O, indirect_result_t<F&, projected<iterator_t<R>, Proj>>>
+    constexpr ranges::unary_transform_result<borrowed_iterator_t<R>, O>
+      transform(R&& r, O result, F op, Proj proj = {});                             // since C++20
+
+  template<input_iterator I1, sentinel_for<I1> S1, input_iterator I2, sentinel_for<I2> S2,
+           weakly_incrementable O, copy_constructible F, class Proj1 = identity,
+           class Proj2 = identity>
+    requires indirectly_writable<O, indirect_result_t<F&, projected<I1, Proj1>,
+                                           projected<I2, Proj2>>>
+    constexpr ranges::binary_transform_result<I1, I2, O>
+      transform(I1 first1, S1 last1, I2 first2, S2 last2, O result,
+                        F binary_op, Proj1 proj1 = {}, Proj2 proj2 = {});           // since C++20
+
+  template<input_range R1, input_range R2, weakly_incrementable O,
+           copy_constructible F, class Proj1 = identity, class Proj2 = identity>
+    requires indirectly_writable<O, indirect_result_t<F&, projected<iterator_t<R1>, Proj1>,
+                                           projected<iterator_t<R2>, Proj2>>>
+    constexpr ranges::binary_transform_result<borrowed_iterator_t<R1>, borrowed_iterator_t<R2>, O>
+      transform(R1&& r1, R2&& r2, O result,
+                        F binary_op, Proj1 proj1 = {}, Proj2 proj2 = {});           // since C++20
 }
 
     constexpr bool     // constexpr in C++20
@@ -836,6 +871,7 @@
 #include <__algorithm/ranges_min_element.h>
 #include <__algorithm/ranges_mismatch.h>
 #include <__algorithm/ranges_swap_ranges.h>
+#include <__algorithm/ranges_transform.h>
 #include <__algorithm/remove.h>
 #include <__algorithm/remove_copy.h>
 #include <__algorithm/remove_copy_if.h>
diff --git a/libcxx/include/module.modulemap b/libcxx/include/module.modulemap
--- a/libcxx/include/module.modulemap
+++ b/libcxx/include/module.modulemap
@@ -303,6 +303,7 @@
       module ranges_min_element       { private header "__algorithm/ranges_min_element.h" }
       module ranges_mismatch          { private header "__algorithm/ranges_mismatch.h" }
       module ranges_swap_ranges       { private header "__algorithm/ranges_swap_ranges.h" }
+      module ranges_transform         { private header "__algorithm/ranges_transform.h" }
       module remove                   { private header "__algorithm/remove.h" }
       module remove_copy              { private header "__algorithm/remove_copy.h" }
       module remove_copy_if           { private header "__algorithm/remove_copy_if.h" }
diff --git a/libcxx/test/libcxx/private_headers.verify.cpp b/libcxx/test/libcxx/private_headers.verify.cpp
--- a/libcxx/test/libcxx/private_headers.verify.cpp
+++ b/libcxx/test/libcxx/private_headers.verify.cpp
@@ -112,6 +112,7 @@
 #include <__algorithm/ranges_min_element.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_min_element.h'}}
 #include <__algorithm/ranges_mismatch.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_mismatch.h'}}
 #include <__algorithm/ranges_swap_ranges.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_swap_ranges.h'}}
+#include <__algorithm/ranges_transform.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_transform.h'}}
 #include <__algorithm/remove.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/remove.h'}}
 #include <__algorithm/remove_copy.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/remove_copy.h'}}
 #include <__algorithm/remove_copy_if.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/remove_copy_if.h'}}
diff --git a/libcxx/test/std/algorithms/alg.modifying.operations/alg.transform/ranges.transform.pass.cpp b/libcxx/test/std/algorithms/alg.modifying.operations/alg.transform/ranges.transform.pass.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/std/algorithms/alg.modifying.operations/alg.transform/ranges.transform.pass.cpp
@@ -0,0 +1,583 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-has-no-incomplete-ranges
+
+// <algorithm>
+
+// template<input_iterator I, sentinel_for<I> S, weakly_incrementable O,
+//          copy_constructible F, class Proj = identity>
+//   requires indirectly_writable<O, indirect_result_t<F&, projected<I, Proj>>>
+//   constexpr ranges::unary_transform_result<I, O>
+//     ranges::transform(I first1, S last1, O result, F op, Proj proj = {});
+// template<input_range R, weakly_incrementable O, copy_constructible F,
+//          class Proj = identity>
+//   requires indirectly_writable<O, indirect_result_t<F&, projected<iterator_t<R>, Proj>>>
+//   constexpr ranges::unary_transform_result<borrowed_iterator_t<R>, O>
+//     ranges::transform(R&& r, O result, F op, Proj proj = {});
+// template<input_iterator I1, sentinel_for<I1> S1, input_iterator I2, sentinel_for<I2> S2,
+//          weakly_incrementable O, copy_constructible F, class Proj1 = identity,
+//          class Proj2 = identity>
+//   requires indirectly_writable<O, indirect_result_t<F&, projected<I1, Proj1>,
+//                                          projected<I2, Proj2>>>
+//   constexpr ranges::binary_transform_result<I1, I2, O>
+//     ranges::transform(I1 first1, S1 last1, I2 first2, S2 last2, O result,
+//                       F binary_op, Proj1 proj1 = {}, Proj2 proj2 = {});
+// template<input_range R1, input_range R2, weakly_incrementable O,
+//          copy_constructible F, class Proj1 = identity, class Proj2 = identity>
+//   requires indirectly_writable<O, indirect_result_t<F&, projected<iterator_t<R1>, Proj1>,
+//                                          projected<iterator_t<R2>, Proj2>>>
+//   constexpr ranges::binary_transform_result<borrowed_iterator_t<R1>, borrowed_iterator_t<R2>, O>
+//     ranges::transform(R1&& r1, R2&& r2, O result,
+//                       F binary_op, Proj1 proj1 = {}, Proj2 proj2 = {});
+
+#include <algorithm>
+#include <array>
+#include <cassert>
+#include <ranges>
+
+#include "test_iterators.h"
+#include "almost_satisfies_types.h"
+
+struct BinaryFunc {
+  int operator()(int, int);
+};
+
+template <class Range>
+concept HasTranformR = requires(Range r, int* out) {
+  std::ranges::transform(r, out, std::identity{});
+  std::ranges::transform(r, r, out, BinaryFunc{});
+};
+static_assert(HasTranformR<std::array<int, 1>>);
+static_assert(!HasTranformR<int>);
+static_assert(!HasTranformR<InputRangeNotDerivedFrom>);
+static_assert(!HasTranformR<InputRangeNotIndirectlyReadable>);
+static_assert(!HasTranformR<InputRangeNotInputOrOutputIterator>);
+static_assert(!HasTranformR<InputRangeNotSentinelSemiregular>);
+static_assert(!HasTranformR<InputRangeNotSentinelEqualityComparableWith>);
+
+template <class It, class Sent = It>
+concept HasTransformIt = requires(It it, Sent sent, int* out) {
+  std::ranges::transform(it, sent, out, std::identity{});
+  std::ranges::transform(it, sent, it, sent, out, BinaryFunc{});
+};
+static_assert(HasTransformIt<int*>);
+static_assert(!HasTransformIt<InputIteratorNotDerivedFrom>);
+static_assert(!HasTransformIt<InputIteratorNotIndirectlyReadable>);
+static_assert(!HasTransformIt<InputIteratorNotInputOrOutputIterator>);
+static_assert(!HasTransformIt<cpp20_input_iterator<int*>, SentinelForNotSemiregular>);
+static_assert(!HasTransformIt<cpp20_input_iterator<int*>, InputRangeNotSentinelEqualityComparableWith>);
+
+template <class It>
+concept HasTransformOut = requires(int* it, int* sent, It out, std::array<int, 2> range) {
+  std::ranges::transform(it, sent, out, std::identity{});
+  std::ranges::transform(it, sent, it, sent, out, BinaryFunc{});
+  std::ranges::transform(range, out, std::identity{});
+  std::ranges::transform(range, range, out, BinaryFunc{});
+};
+static_assert(HasTransformOut<int*>);
+static_assert(!HasTransformOut<WeaklyIncrementableNotMovable>);
+
+// check indirectly_readable
+static_assert(HasTransformOut<char*>);
+static_assert(!HasTransformOut<int**>);
+
+struct MoveOnlyFunctor {
+  MoveOnlyFunctor(const MoveOnlyFunctor&) = delete;
+  MoveOnlyFunctor(MoveOnlyFunctor&&) = default;
+  int operator()(int);
+  int operator()(int, int);
+};
+
+template <class Func>
+concept HasTransformFuncUnary = requires(int* it, int* sent, int* out, std::array<int, 2> range, Func func) {
+  std::ranges::transform(it, sent, out, func);
+  std::ranges::transform(range, out, func);
+};
+static_assert(HasTransformFuncUnary<std::identity>);
+static_assert(!HasTransformFuncUnary<MoveOnlyFunctor>);
+
+template <class Func>
+concept HasTransformFuncBinary = requires(int* it, int* sent, int* out, std::array<int, 2> range, Func func) {
+  std::ranges::transform(it, sent, it, sent, out, func);
+  std::ranges::transform(range, range, out, func);
+};
+static_assert(HasTransformFuncBinary<BinaryFunc>);
+static_assert(!HasTransformFuncBinary<MoveOnlyFunctor>);
+
+static_assert(std::is_same_v<std::ranges::unary_transform_result<int, long>, std::ranges::in_out_result<int, long>>);
+static_assert(std::is_same_v<std::ranges::binary_transform_result<int, long, char>,
+                             std::ranges::in_in_out_result<int, long, char>>);
+
+template <class In1, class In2, class Out, class Sent1, class Sent2>
+constexpr bool test_iterators() {
+  { // simple
+    { // unary
+      {
+        int a[] = {1, 2, 3, 4, 5};
+        int b[5];
+        std::same_as<std::ranges::in_out_result<In1, Out>> decltype(auto) ret =
+          std::ranges::transform(In1(a), Sent1(In1(a + 5)), Out(b), [](int i) { return i * 2; });
+        assert((std::to_array(b) == std::array{2, 4, 6, 8, 10}));
+        assert(base(ret.in) == a + 5);
+        assert(base(ret.out) == b + 5);
+      }
+
+      {
+        int a[] = {1, 2, 3, 4, 5};
+        int b[5];
+        auto range = std::ranges::subrange(In1(a), Sent1(In1(a + 5)));
+        std::same_as<std::ranges::in_out_result<In1, Out>> decltype(auto) ret =
+          std::ranges::transform(range, Out(b), [](int i) { return i * 2; });
+        assert((std::to_array(b) == std::array{2, 4, 6, 8, 10}));
+        assert(base(ret.in) == a + 5);
+        assert(base(ret.out) == b + 5);
+      }
+    }
+
+    { // binary
+      {
+        int a[] = {1, 2, 3, 4, 5};
+        int b[] = {5, 4, 3, 2, 1};
+        int c[5];
+
+        std::same_as<std::ranges::in_in_out_result<In1, In2, Out>> decltype(auto) ret = std::ranges::transform(
+            In1(a), Sent1(In1(a + 5)), In2(b), Sent2(In2(b + 5)), Out(c), [](int i, int j) { return i + j; });
+
+        assert((std::to_array(c) == std::array{6, 6, 6, 6, 6}));
+        assert(base(ret.in1) == a + 5);
+        assert(base(ret.in2) == b + 5);
+        assert(base(ret.out) == c + 5);
+      }
+
+      {
+        int a[] = {1, 2, 3, 4, 5};
+        int b[] = {5, 4, 3, 2, 1};
+        int c[5];
+
+        auto range1 = std::ranges::subrange(In1(a), Sent1(In1(a + 5)));
+        auto range2 = std::ranges::subrange(In2(b), Sent2(In2(b + 5)));
+
+        std::same_as<std::ranges::in_in_out_result<In1, In2, Out>> decltype(auto) ret = std::ranges::transform(
+            range1, range2, Out(c), [](int i, int j) { return i + j; });
+
+        assert((std::to_array(c) == std::array{6, 6, 6, 6, 6}));
+        assert(base(ret.in1) == a + 5);
+        assert(base(ret.in2) == b + 5);
+        assert(base(ret.out) == c + 5);
+      }
+    }
+  }
+
+  { // first range empty
+    { // unary
+      {
+        int a[] = {};
+        int b[5];
+        auto ret = std::ranges::transform(In1(a), Sent1(In1(a)), Out(b), [](int i) { return i * 2; });
+        assert(base(ret.in) == a);
+        assert(base(ret.out) == b);
+      }
+
+      {
+        int a[] = {};
+        int b[5];
+        auto range = std::ranges::subrange(In1(a), Sent1(In1(a)));
+        auto ret = std::ranges::transform(range, Out(b), [](int i) { return i * 2; });
+        assert(base(ret.in) == a);
+        assert(base(ret.out) == b);
+      }
+    }
+
+    { // binary
+      {
+        int a[] = {};
+        int b[] = {5, 4, 3, 2, 1};
+        int c[5];
+
+        auto ret = std::ranges::transform(
+            In1(a), Sent1(In1(a)), In2(b), Sent2(In2(b + 5)), Out(c), [](int i, int j) { return i + j; });
+
+        assert(base(ret.in1) == a);
+        assert(base(ret.in2) == b);
+        assert(base(ret.out) == c);
+      }
+
+      {
+        int a[] = {};
+        int b[] = {5, 4, 3, 2, 1};
+        int c[5];
+
+        auto range1 = std::ranges::subrange(In1(a), Sent1(In1(a)));
+        auto range2 = std::ranges::subrange(In2(b), Sent2(In2(b + 5)));
+
+        auto ret = std::ranges::transform(range1, range2, Out(c), [](int i, int j) { return i + j; });
+
+        assert(base(ret.in1) == a);
+        assert(base(ret.in2) == b);
+        assert(base(ret.out) == c);
+      }
+    }
+  }
+
+  { // second range empty (binary)
+    {
+      int a[] = {5, 4, 3, 2, 1};
+      int b[] = {};
+      int c[5];
+
+      auto ret = std::ranges::transform(
+          In1(a), Sent1(In1(a + 5)), In2(b), Sent2(In2(b)), Out(c), [](int i, int j) { return i + j; });
+
+      assert(base(ret.in1) == a);
+      assert(base(ret.in2) == b);
+      assert(base(ret.out) == c);
+    }
+
+    {
+      int a[] = {5, 4, 3, 2, 1};
+      int b[] = {};
+      int c[5];
+
+      auto range1 = std::ranges::subrange(In1(a), Sent1(In1(a + 5)));
+      auto range2 = std::ranges::subrange(In2(b), Sent2(In2(b)));
+
+      auto ret = std::ranges::transform(range1, range2, Out(c), [](int i, int j) { return i + j; });
+
+      assert(base(ret.in1) == a);
+      assert(base(ret.in2) == b);
+      assert(base(ret.out) == c);
+    }
+  }
+
+  { // both ranges empty (binary)
+    {
+      int a[] = {};
+      int b[] = {};
+      int c[5];
+
+      auto ret = std::ranges::transform(
+          In1(a), Sent1(In1(a)), In2(b), Sent2(In2(b)), Out(c), [](int i, int j) { return i + j; });
+
+      assert(base(ret.in1) == a);
+      assert(base(ret.in2) == b);
+      assert(base(ret.out) == c);
+    }
+
+    {
+      int a[] = {};
+      int b[] = {};
+      int c[5];
+
+      auto range1 = std::ranges::subrange(In1(a), Sent1(In1(a)));
+      auto range2 = std::ranges::subrange(In2(b), Sent2(In2(b)));
+
+      auto ret = std::ranges::transform(range1, range2, Out(c), [](int i, int j) { return i + j; });
+
+      assert(base(ret.in1) == a);
+      assert(base(ret.in2) == b);
+      assert(base(ret.out) == c);
+    }
+  }
+
+  { // first range one element
+    { // unary
+      {
+        int a[] = {2};
+        int b[5];
+        auto ret = std::ranges::transform(In1(a), Sent1(In1(a + 1)), Out(b), [](int i) { return i * 2; });
+        assert(b[0] == 4);
+        assert(base(ret.in) == a + 1);
+        assert(base(ret.out) == b + 1);
+      }
+
+      {
+        int a[] = {2};
+        int b[5];
+        auto range = std::ranges::subrange(In1(a), Sent1(In1(a + 1)));
+        auto ret = std::ranges::transform(range, Out(b), [](int i) { return i * 2; });
+        assert(b[0] == 4);
+        assert(base(ret.in) == a + 1);
+        assert(base(ret.out) == b + 1);
+      }
+    }
+
+    { // binary
+      {
+        int a[] = {2};
+        int b[] = {5, 4, 3, 2, 1};
+        int c[5];
+
+        auto ret = std::ranges::transform(
+            In1(a), Sent1(In1(a + 1)), In2(b), Sent2(In2(b + 5)), Out(c), [](int i, int j) { return i + j; });
+
+        assert(c[0] == 7);
+        assert(base(ret.in1) == a + 1);
+        assert(base(ret.in2) == b + 1);
+        assert(base(ret.out) == c + 1);
+      }
+
+      {
+        int a[] = {2};
+        int b[] = {5, 4, 3, 2, 1};
+        int c[5];
+
+        auto range1 = std::ranges::subrange(In1(a), Sent1(In1(a + 1)));
+        auto range2 = std::ranges::subrange(In2(b), Sent2(In2(b + 5)));
+
+        auto ret = std::ranges::transform(range1, range2, Out(c), [](int i, int j) { return i + j; });
+
+        assert(c[0] == 7);
+        assert(base(ret.in1) == a + 1);
+        assert(base(ret.in2) == b + 1);
+        assert(base(ret.out) == c + 1);
+      }
+    }
+  }
+
+  { // second range contains one element (binary)
+    {
+      int a[] = {5, 4, 3, 2, 1};
+      int b[] = {4};
+      int c[5];
+
+      auto ret = std::ranges::transform(
+          In1(a), Sent1(In1(a + 5)), In2(b), Sent2(In2(b + 1)), Out(c), [](int i, int j) { return i + j; });
+
+      assert(c[0] == 9);
+      assert(base(ret.in1) == a + 1);
+      assert(base(ret.in2) == b + 1);
+      assert(base(ret.out) == c + 1);
+    }
+
+    {
+      int a[] = {5, 4, 3, 2, 1};
+      int b[] = {4};
+      int c[5];
+
+      auto range1 = std::ranges::subrange(In1(a), Sent1(In1(a + 5)));
+      auto range2 = std::ranges::subrange(In2(b), Sent2(In2(b + 1)));
+
+      auto ret = std::ranges::transform(range1, range2, Out(c), [](int i, int j) { return i + j; });
+
+      assert(c[0] == 9);
+      assert(base(ret.in1) == a + 1);
+      assert(base(ret.in2) == b + 1);
+      assert(base(ret.out) == c + 1);
+    }
+  }
+
+  { // check that the transform function and projection call counts are correct
+    { // unary
+      {
+        int predCount = 0;
+        int projCount = 0;
+        auto pred = [&](int) { ++predCount; return 1; };
+        auto proj = [&](int) { ++projCount; return 0; };
+        int a[] = {1, 2, 3, 4};
+        std::array<int, 4> c;
+        std::ranges::transform(In1(a), Sent1(In1(a + 4)), Out(c.data()), pred, proj);
+        assert(predCount == 4);
+        assert(projCount == 4);
+        assert((c == std::array{1, 1, 1, 1}));
+      }
+      {
+        int predCount = 0;
+        int projCount = 0;
+        auto pred = [&](int) { ++predCount; return 1; };
+        auto proj = [&](int) { ++projCount; return 0; };
+        int a[] = {1, 2, 3, 4};
+        std::array<int, 4> c;
+        auto range = std::ranges::subrange(In1(a), Sent1(In1(a + 4)));
+        std::ranges::transform(range, Out(c.data()), pred, proj);
+        assert(predCount == 4);
+        assert(projCount == 4);
+        assert((c == std::array{1, 1, 1, 1}));
+      }
+    }
+    { // binary
+      {
+        int predCount = 0;
+        int proj1Count = 0;
+        int proj2Count = 0;
+        auto pred = [&](int, int) { ++predCount; return 1; };
+        auto proj1 = [&](int) { ++proj1Count; return 0; };
+        auto proj2 = [&](int) { ++proj2Count; return 0; };
+        int a[] = {1, 2, 3, 4};
+        int b[] = {1, 2, 3, 4};
+        std::array<int, 4> c;
+        std::ranges::transform(In1(a), Sent1(In1(a + 4)), In2(b), Sent2(In2(b + 4)), Out(c.data()), pred, proj1, proj2);
+        assert(predCount == 4);
+        assert(proj1Count == 4);
+        assert(proj2Count == 4);
+        assert((c == std::array{1, 1, 1, 1}));
+      }
+      {
+        int predCount = 0;
+        int proj1Count = 0;
+        int proj2Count = 0;
+        auto pred = [&](int, int) { ++predCount; return 1; };
+        auto proj1 = [&](int) { ++proj1Count; return 0; };
+        auto proj2 = [&](int) { ++proj2Count; return 0; };
+        int a[] = {1, 2, 3, 4};
+        int b[] = {1, 2, 3, 4};
+        std::array<int, 4> c;
+        auto range1 = std::ranges::subrange(In1(a), Sent1(In1(a + 4)));
+        auto range2 = std::ranges::subrange(In2(b), Sent2(In2(b + 4)));
+        std::ranges::transform(range1, range2, Out(c.data()), pred, proj1, proj2);
+        assert(predCount == 4);
+        assert(proj1Count == 4);
+        assert(proj2Count == 4);
+        assert((c == std::array{1, 1, 1, 1}));
+      }
+    }
+  }
+
+  return true;
+}
+
+template <class In2, class Out, class Sent2 = In2>
+constexpr void test_iterator_in1() {
+  test_iterators<cpp17_input_iterator<int*>, In2, Out, sentinel_wrapper<cpp17_input_iterator<int*>>, Sent2>();
+  test_iterators<cpp20_input_iterator<int*>, In2, Out, sentinel_wrapper<cpp20_input_iterator<int*>>, Sent2>();
+  test_iterators<forward_iterator<int*>, In2, Out, forward_iterator<int*>, Sent2>();
+  test_iterators<bidirectional_iterator<int*>, In2, Out, bidirectional_iterator<int*>, Sent2>();
+  test_iterators<random_access_iterator<int*>, In2, Out, random_access_iterator<int*>, Sent2>();
+  test_iterators<contiguous_iterator<int*>, In2, Out, contiguous_iterator<int*>, Sent2>();
+  test_iterators<int*, In2, Out, int*, Sent2>();
+  // static_asserting here to avoid hitting the constant evaluation step limit
+  static_assert(test_iterators<cpp17_input_iterator<int*>, In2, Out, sentinel_wrapper<cpp17_input_iterator<int*>>, Sent2>());
+  static_assert(test_iterators<cpp20_input_iterator<int*>, In2, Out, sentinel_wrapper<cpp20_input_iterator<int*>>, Sent2>());
+  static_assert(test_iterators<forward_iterator<int*>, In2, Out, forward_iterator<int*>, Sent2>());
+  static_assert(test_iterators<bidirectional_iterator<int*>, In2, Out, bidirectional_iterator<int*>, Sent2>());
+  static_assert(test_iterators<random_access_iterator<int*>, In2, Out, random_access_iterator<int*>, Sent2>());
+  static_assert(test_iterators<contiguous_iterator<int*>, In2, Out, contiguous_iterator<int*>, Sent2>());
+  static_assert(test_iterators<int*, In2, Out, int*, Sent2>());
+}
+
+template <class Out>
+void test_iterators_in1_in2() {
+  test_iterator_in1<cpp17_input_iterator<int*>, Out, sentinel_wrapper<cpp17_input_iterator<int*>>>();
+  test_iterator_in1<cpp20_input_iterator<int*>, Out, sentinel_wrapper<cpp20_input_iterator<int*>>>();
+  test_iterator_in1<forward_iterator<int*>, Out>();
+  test_iterator_in1<bidirectional_iterator<int*>, Out>();
+  test_iterator_in1<random_access_iterator<int*>, Out>();
+  test_iterator_in1<contiguous_iterator<int*>, Out>();
+  test_iterator_in1<int*, Out>();
+}
+
+constexpr bool test() {
+  { // check that std::ranges::dangling is returned properly
+    { // unary
+      std::array<int, 5> b;
+      std::same_as<std::ranges::in_out_result<std::ranges::dangling, int*>> auto ret =
+          std::ranges::transform(std::array{1, 2, 3, 5, 4}, b.data(), [](int i) { return i * i; });
+      assert((b == std::array{1, 4, 9, 25, 16}));
+      assert(ret.out == b.data() + b.size());
+    }
+    // binary
+    {
+      int b[] = {2, 5, 4, 3, 1};
+      std::array<int, 5> c;
+      std::same_as<std::ranges::in_in_out_result<std::ranges::dangling, int*, int*>> auto ret =
+          std::ranges::transform(std::array{1, 2, 3, 5, 4}, b, c.data(), [](int i, int j) { return i * j; });
+      assert((c == std::array{2, 10, 12, 15, 4}));
+      assert(ret.in2 == b + 5);
+      assert(ret.out == c.data() + c.size());
+    }
+    {
+      int a[] = {2, 5, 4, 3, 1, 4, 5, 6};
+      std::array<int, 8> c;
+      std::same_as<std::ranges::in_in_out_result<int*, std::ranges::dangling, int*>> auto ret =
+          std::ranges::transform(a, std::array{1, 2, 3, 5, 4, 5, 6, 7}, c.data(), [](int i, int j) { return i * j; });
+      assert((c == std::array{2, 10, 12, 15, 4, 20, 30, 42}));
+      assert(ret.in1 == a + 8);
+      assert(ret.out == c.data() + c.size());
+    }
+    {
+      std::array<int, 3> c;
+      std::same_as<std::ranges::in_in_out_result<std::ranges::dangling, std::ranges::dangling, int*>> auto ret =
+          std::ranges::transform(std::array{4, 4, 4}, std::array{4, 4, 4}, c.data(), [](int i, int j) { return i * j; });
+      assert((c == std::array{16, 16, 16}));
+      assert(ret.out == c.data() + c.size());
+    }
+  }
+
+  { // check that returning another type from the projection works
+    { // unary
+      {
+        struct S { int i; int other; };
+        S a[] = { S{0, 0}, S{1, 0}, S{3, 0}, S{10, 0} };
+        std::array<int, 4> b;
+        std::ranges::transform(a, a + 4, b.begin(), [](S s) { return s.i; });
+        assert((b == std::array{0, 1, 3, 10}));
+      }
+      {
+        struct S { int i; int other; };
+        S a[] = { S{0, 0}, S{1, 0}, S{3, 0}, S{10, 0} };
+        std::array<int, 4> b;
+        std::ranges::transform(a, b.begin(), [](S s) { return s.i; });
+        assert((b == std::array{0, 1, 3, 10}));
+      }
+    }
+    { // binary
+      {
+        struct S { int i; int other; };
+        S a[] = { S{0, 0}, S{1, 0}, S{3, 0}, S{10, 0} };
+        S b[] = { S{0, 10}, S{1, 20}, S{3, 30}, S{10, 40} };
+        std::array<int, 4> c;
+        std::ranges::transform(a, a + 4, b, b + 4, c.begin(), [](S s1, S s2) { return s1.i + s2.other; });
+        assert((c == std::array{10, 21, 33, 50}));
+      }
+      {
+        struct S { int i; int other; };
+        S a[] = { S{0, 0}, S{1, 0}, S{3, 0}, S{10, 0} };
+        S b[] = { S{0, 10}, S{1, 20}, S{3, 30}, S{10, 40} };
+        std::array<int, 4> c;
+        std::ranges::transform(a, b, c.begin(), [](S s1, S s2) { return s1.i + s2.other; });
+        assert((c == std::array{10, 21, 33, 50}));
+      }
+    }
+  }
+
+  { // check that std::invoke is used
+    { // unary
+      struct S { int i; };
+      S a[] = { S{1}, S{3}, S{2} };
+      std::array<int, 3> b;
+      auto ret = std::ranges::transform(a, b.data(), [](int i) { return i; }, &S::i);
+      assert((b == std::array{1, 3, 2}));
+      assert(ret.out == b.data() + 3);
+    }
+    { // binary
+      struct S { int i; };
+      S a[] = { S{1}, S{3}, S{2} };
+      S b[] = { S{2}, S{5}, S{3} };
+      std::array<int, 3> c;
+      auto ret = std::ranges::transform(a, b, c.data(), [](int i, int j) { return i + j + 2; }, &S::i, &S::i);
+      assert((c == std::array{5, 10, 7}));
+      assert(ret.out == c.data() + 3);
+    }
+  }
+
+  return true;
+}
+
+int main(int, char**) {
+  test_iterators_in1_in2<cpp17_output_iterator<int*>>();
+  test_iterators_in1_in2<forward_iterator<int*>>();
+  test_iterators_in1_in2<bidirectional_iterator<int*>>();
+  test_iterators_in1_in2<random_access_iterator<int*>>();
+  test_iterators_in1_in2<contiguous_iterator<int*>>();
+  test_iterators_in1_in2<int*>();
+  test();
+  static_assert(test());
+
+  return 0;
+}
diff --git a/libcxx/test/support/almost_satisfies_types.h b/libcxx/test/support/almost_satisfies_types.h
--- a/libcxx/test/support/almost_satisfies_types.h
+++ b/libcxx/test/support/almost_satisfies_types.h
@@ -128,4 +128,15 @@
 static_assert(std::semiregular<SentinelForNotWeaklyEqualityComparableWith>);
 static_assert(!std::sentinel_for<SentinelForNotWeaklyEqualityComparableWith, cpp20_input_iterator<int*>>);
 
+class WeaklyIncrementableNotMovable {
+public:
+  using difference_type = long;
+  WeaklyIncrementableNotMovable& operator++();
+  void operator++(int);
+  WeaklyIncrementableNotMovable(const WeaklyIncrementableNotMovable&) = delete;
+};
+
+static_assert(!std::movable<WeaklyIncrementableNotMovable>);
+static_assert(!std::weakly_incrementable<WeaklyIncrementableNotMovable>);
+
 #endif // ALMOST_SATISFIES_TYPES_H