diff --git a/libcxx/include/CMakeLists.txt b/libcxx/include/CMakeLists.txt
--- a/libcxx/include/CMakeLists.txt
+++ b/libcxx/include/CMakeLists.txt
@@ -61,6 +61,7 @@
   __algorithm/pop_heap.h
   __algorithm/prev_permutation.h
   __algorithm/push_heap.h
+  __algorithm/ranges_mismatch.h
   __algorithm/remove.h
   __algorithm/remove_copy.h
   __algorithm/remove_copy_if.h
diff --git a/libcxx/include/__algorithm/ranges_mismatch.h b/libcxx/include/__algorithm/ranges_mismatch.h
new file mode 100644
--- /dev/null
+++ b/libcxx/include/__algorithm/ranges_mismatch.h
@@ -0,0 +1,77 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_MISMATCH_H
+#define _LIBCPP___ALGORITHM_RANGES_MISMATCH_H
+
+#include <__algorithm/in_in_result.h>
+#include <__config>
+#include <__functional/identity.h>
+#include <__functional/ranges_operations.h>
+#include <__iterator/concepts.h>
+#include <__iterator/indirectly_comparable.h>
+#include <ranges>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+namespace ranges {
+
+template <class _I1, class _I2>
+using mismatch_result = in_in_result<_I1, _I2>;
+
+namespace __mismatch {
+struct __fn {
+  template <input_iterator _I1, sentinel_for<_I1> _S1,
+            input_iterator _I2, sentinel_for<_I2> _S2,
+            class _Pred = ranges::equal_to, class _Proj1 = identity, class _Proj2 = identity>
+    requires indirectly_comparable<_I1, _I2, _Pred, _Proj1, _Proj2>
+  _LIBCPP_HIDE_FROM_ABI constexpr
+  ranges::mismatch_result<_I1, _I2> operator()(_I1 __first1,
+                                               _S1 __last1,
+                                               _I2 __first2,
+                                               _S2 __last2,
+                                               _Pred __pred = {},
+                                               _Proj1 __proj1 = {},
+                                               _Proj2 __proj2 = {}) const {
+    while (__first1 != __last1 && __first2 != __last2) {
+      if (!invoke(__pred, invoke(__proj1, *__first1), invoke(__proj2, *__first2)))
+        break;
+      ++__first1;
+      ++__first2;
+    }
+    return {__first1, __first2};
+  }
+
+  template <input_range _R1, input_range _R2,
+            class _Pred = ranges::equal_to, class _Proj1 = identity, class _Proj2 = identity>
+    requires indirectly_comparable<iterator_t<_R1>, iterator_t<_R2>, _Pred, _Proj1, _Proj2>
+  _LIBCPP_HIDE_FROM_ABI constexpr ranges::mismatch_result<borrowed_iterator_t<_R1>, borrowed_iterator_t<_R2>>
+      operator()(_R1&& __r1, _R2&& __r2, _Pred&& __pred = {}, _Proj1&& __proj1 = {}, _Proj2&& __proj2 = {}) const {
+    return operator()(ranges::begin(__r1),
+                      ranges::end(__r1),
+                      ranges::begin(__r2),
+                      ranges::end(__r2),
+                      std::forward<_Pred>(__pred),
+                      std::forward<_Proj1>(__proj1),
+                      std::forward<_Proj2>(__proj2));
+  }
+};
+} // namespace __mismatch
+
+inline namespace __cpo {
+  constexpr inline auto mismatch = __mismatch::__fn{};
+} // namespace __cpo
+} // namespace ranges
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___ALGORITHM_RANGES_MISMATCH_H
diff --git a/libcxx/include/algorithm b/libcxx/include/algorithm
--- a/libcxx/include/algorithm
+++ b/libcxx/include/algorithm
@@ -731,6 +731,7 @@
 #include <__algorithm/pop_heap.h>
 #include <__algorithm/prev_permutation.h>
 #include <__algorithm/push_heap.h>
+#include <__algorithm/ranges_mismatch.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
@@ -281,6 +281,7 @@
       module pop_heap                 { private header "__algorithm/pop_heap.h" }
       module prev_permutation         { private header "__algorithm/prev_permutation.h" }
       module push_heap                { private header "__algorithm/push_heap.h" }
+      module rnages_mismatch          { private header "__algorithm/ranges_mismatch.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/diagnostics/detail.headers/algorithm/ranges_mismatch.module.verify.cpp b/libcxx/test/libcxx/diagnostics/detail.headers/algorithm/ranges_mismatch.module.verify.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/libcxx/diagnostics/detail.headers/algorithm/ranges_mismatch.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_mismatch.h'}}
+#include <__algorithm/ranges_mismatch.h>
diff --git a/libcxx/test/std/algorithms/alg.nonmodifying/mismatch/ranges_mismatch.pass.cpp b/libcxx/test/std/algorithms/alg.nonmodifying/mismatch/ranges_mismatch.pass.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/std/algorithms/alg.nonmodifying/mismatch/ranges_mismatch.pass.cpp
@@ -0,0 +1,109 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+
+#include <algorithm>
+#include <cassert>
+
+#include "test_iterators.h"
+
+template <class Iter1, class Iter2>
+constexpr void test_iterators(Iter1 begin1, Iter1 end1, Iter2 begin2, Iter2 end2, Iter1 expected1, Iter2 expected2) {
+  using Expected = std::ranges::mismatch_result<Iter1, Iter2>;
+  std::same_as<Expected> auto ret = std::ranges::mismatch(begin1, end1, begin2, end2);
+  assert(ret.in1 == expected1);
+  assert(ret.in2 == expected2);
+}
+
+template <class Range1, class Range2, class Iter1, class Iter2>
+constexpr void test_ranges(Range1& r1, Range2& r2, Iter1 expected1, Iter2 expected2) {
+  using Expected = std::ranges::mismatch_result<Iter1, Iter2>;
+  std::same_as<Expected> auto ret = std::ranges::mismatch(r1, r2);
+  assert(ret.in1 == expected1);
+  assert(ret.in2 == expected2);
+}
+
+template <class Iter1, class Iter2>
+constexpr void test_iters() {
+  int a[] = {1, 2, 3, 4, 5};
+  int b[] = {1, 2, 3, 5, 4};
+
+  test_iterators(Iter1(a), Iter1(a + 5), Iter2(b), Iter2(b + 5), Iter1(a + 3), Iter2(b + 3));
+}
+
+constexpr void test_sentinel() {
+  int a[] = {1, 2, 3, 4, 5};
+  int b[] = {1, 2, 3, 5, 4};
+
+  using Iter = int*;
+  using Sentinel = sentinel_wrapper<Iter>;
+  using Expected = std::ranges::mismatch_result<Iter, Iter>;
+
+  std::same_as<Expected> auto r = std::ranges::mismatch(Iter(a), Sentinel(a + 5), Iter(b), Sentinel(b + 5));
+  assert(r.in1 == a + 3);
+  assert(r.in2 == b + 3);
+}
+
+constexpr void test_different_lengths() {
+  std::array<int, 3> a = {1, 2, 3};
+  std::array<int, 2> b = {1, 2};
+
+  test_iterators(a.begin(), a.begin() + 3, b.begin(), b.begin() + 2, a.begin() + 2, b.begin() + 2);
+  test_ranges(a, b, a.begin() + 2, b.begin() + 2);
+}
+
+constexpr void test_borrowed_range() {
+  int r1[] = {1, 2, 3, 4, 5};
+  int r2[] = {1, 2, 3, 5, 4};
+
+  using Iter = int*;
+  using Sentinel = sentinel_wrapper<Iter>;
+
+  std::ranges::subrange b1{Iter(r1), Sentinel(Iter(r1 + 5))};
+  std::ranges::subrange b2{Iter(r2), Sentinel(Iter(r2 + 5))};
+
+  test_ranges(b1, b2, Iter(r1 + 3), Iter(r2 + 3));
+}
+
+constexpr bool test() {
+  test_iters<forward_iterator<int*>, forward_iterator<int*>>();
+  test_iters<forward_iterator<int*>, bidirectional_iterator<int*>>();
+  test_iters<forward_iterator<int*>, random_access_iterator<int*>>();
+  test_iters<forward_iterator<int*>, int*>();
+
+  test_iters<bidirectional_iterator<int*>, forward_iterator<int*>>();
+  test_iters<bidirectional_iterator<int*>, bidirectional_iterator<int*>>();
+  test_iters<bidirectional_iterator<int*>, random_access_iterator<int*>>();
+  test_iters<bidirectional_iterator<int*>, int*>();
+
+  test_iters<random_access_iterator<int*>, forward_iterator<int*>>();
+  test_iters<random_access_iterator<int*>, bidirectional_iterator<int*>>();
+  test_iters<random_access_iterator<int*>, random_access_iterator<int*>>();
+  test_iters<random_access_iterator<int*>, int*>();
+
+  test_iters<int*, forward_iterator<int*>>();
+  test_iters<int*, bidirectional_iterator<int*>>();
+  test_iters<int*, random_access_iterator<int*>>();
+  test_iters<int*, int*>();
+
+  std::array<int, 5> a = {1, 2, 3, 4, 5};
+  std::array<int, 5> b = {1, 2, 3, 5, 4};
+  test_ranges(a, b, a.begin() + 3, b.begin() + 3);
+  test_sentinel();
+  test_different_lengths();
+  test_borrowed_range();
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+  static_assert(test());
+  return 0;
+}