diff --git a/libcxx/docs/Cxx2aStatusPaperStatus.csv b/libcxx/docs/Cxx2aStatusPaperStatus.csv
--- a/libcxx/docs/Cxx2aStatusPaperStatus.csv
+++ b/libcxx/docs/Cxx2aStatusPaperStatus.csv
@@ -103,7 +103,7 @@
 "`P0466 <https://wg21.link/P0466>`__","LWG","Layout-compatibility and Pointer-interconvertibility Traits","Cologne","",""
 "`P0553 <https://wg21.link/P0553>`__","LWG","Bit operations","Cologne","|Complete|","9.0"
 "`P0631 <https://wg21.link/P0631>`__","LWG","Math Constants","Cologne","|Complete|","11.0"
-"`P0645 <https://wg21.link/P0645>`__","LWG","Text Formatting","Cologne","",""
+"`P0645 <https://wg21.link/P0645>`__","LWG","Text Formatting","Cologne","|In Progress|",""
 "`P0660 <https://wg21.link/P0660>`__","LWG","Stop Token and Joining Thread, Rev 10","Cologne","",""
 "`P0784 <https://wg21.link/P0784>`__","CWG","More constexpr containers","Cologne","|Complete|","12.0"
 "`P0980 <https://wg21.link/P0980>`__","LWG","Making std::string constexpr","Cologne","",""
diff --git a/libcxx/docs/FeatureTestMacroTable.rst b/libcxx/docs/FeatureTestMacroTable.rst
--- a/libcxx/docs/FeatureTestMacroTable.rst
+++ b/libcxx/docs/FeatureTestMacroTable.rst
@@ -206,6 +206,8 @@
     ------------------------------------------------- -----------------
     ``__cpp_lib_erase_if``                            ``202002L``
     ------------------------------------------------- -----------------
+    ``__cpp_lib_format``                              *unimplemented*
+    ------------------------------------------------- -----------------
     ``__cpp_lib_generic_unordered_lookup``            ``201811L``
     ------------------------------------------------- -----------------
     ``__cpp_lib_int_pow2``                            ``202002L``
diff --git a/libcxx/include/CMakeLists.txt b/libcxx/include/CMakeLists.txt
--- a/libcxx/include/CMakeLists.txt
+++ b/libcxx/include/CMakeLists.txt
@@ -94,6 +94,7 @@
   fenv.h
   filesystem
   float.h
+  format
   forward_list
   fstream
   functional
diff --git a/libcxx/include/format b/libcxx/include/format
new file mode 100644
--- /dev/null
+++ b/libcxx/include/format
@@ -0,0 +1,242 @@
+// -*- C++ -*-
+//===--------------------------- format -----------------------------------===//
+//
+// 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_FORMAT
+#define _LIBCPP_FORMAT
+
+/*
+
+namespace std {
+  // [format.context], class template basic_format_context
+  template<class Out, class charT> class basic_format_context;
+  using format_context = basic_format_context<unspecified, char>;
+  using wformat_context = basic_format_context<unspecified, wchar_t>;
+
+  // [format.args], class template basic_format_args
+  template<class Context> class basic_format_args;
+  using format_args = basic_format_args<format_context>;
+  using wformat_args = basic_format_args<wformat_context>;
+
+  template<class Out, class charT>
+    using format_args_t = basic_format_args<basic_format_context<Out, charT>>;
+
+  // [format.functions], formatting functions
+  template<class... Args>
+    string format(string_view fmt, const Args&... args);
+  template<class... Args>
+    wstring format(wstring_view fmt, const Args&... args);
+  template<class... Args>
+    string format(const locale& loc, string_view fmt, const Args&... args);
+  template<class... Args>
+    wstring format(const locale& loc, wstring_view fmt, const Args&... args);
+
+  string vformat(string_view fmt, format_args args);
+  wstring vformat(wstring_view fmt, wformat_args args);
+  string vformat(const locale& loc, string_view fmt, format_args args);
+  wstring vformat(const locale& loc, wstring_view fmt, wformat_args args);
+
+  template<class Out, class... Args>
+    Out format_to(Out out, string_view fmt, const Args&... args);
+  template<class Out, class... Args>
+    Out format_to(Out out, wstring_view fmt, const Args&... args);
+  template<class Out, class... Args>
+    Out format_to(Out out, const locale& loc, string_view fmt, const Args&... args);
+  template<class Out, class... Args>
+    Out format_to(Out out, const locale& loc, wstring_view fmt, const Args&... args);
+
+  template<class Out>
+    Out vformat_to(Out out, string_view fmt,
+                   format_args_t<type_identity_t<Out>, char> args);
+  template<class Out>
+    Out vformat_to(Out out, wstring_view fmt,
+                   format_args_t<type_identity_t<Out>, wchar_t> args);
+  template<class Out>
+    Out vformat_to(Out out, const locale& loc, string_view fmt,
+                   format_args_t<type_identity_t<Out>, char> args);
+  template<class Out>
+    Out vformat_to(Out out, const locale& loc, wstring_view fmt,
+                   format_args_t<type_identity_t<Out>, wchar_t> args);
+
+  template<class Out> struct format_to_n_result {
+    Out out;
+    iter_difference_t<Out> size;
+  };
+
+ template<class Out, class... Args>
+    format_to_n_result<Out> format_to_n(Out out, iter_difference_t<Out> n,
+                                        string_view fmt, const Args&... args);
+  template<class Out, class... Args>
+    format_to_n_result<Out> format_to_n(Out out, iter_difference_t<Out> n,
+                                        wstring_view fmt, const Args&... args);
+  template<class Out, class... Args>
+    format_to_n_result<Out> format_to_n(Out out, iter_difference_t<Out> n,
+                                        const locale& loc, string_view fmt,
+                                        const Args&... args);
+  template<class Out, class... Args>
+    format_to_n_result<Out> format_to_n(Out out, iter_difference_t<Out> n,
+                                        const locale& loc, wstring_view fmt,
+                                        const Args&... args);
+
+  template<class... Args>
+    size_t formatted_size(string_view fmt, const Args&... args);
+  template<class... Args>
+    size_t formatted_size(wstring_view fmt, const Args&... args);
+  template<class... Args>
+    size_t formatted_size(const locale& loc, string_view fmt, const Args&... args);
+  template<class... Args>
+    size_t formatted_size(const locale& loc, wstring_view fmt, const Args&... args);
+
+  // [format.formatter], formatter
+  template<class T, class charT = char> struct formatter;
+
+  // [format.parse.ctx], class template basic_format_parse_context
+  template<class charT> class basic_format_parse_context;
+  using format_parse_context = basic_format_parse_context<char>;
+  using wformat_parse_context = basic_format_parse_context<wchar_t>;
+
+  // [format.arguments], arguments
+  // [format.arg], class template basic_format_arg
+  template<class Context> class basic_format_arg;
+
+  template<class Visitor, class Context>
+    see below visit_format_arg(Visitor&& vis, basic_format_arg<Context> arg);
+
+  // [format.arg.store], class template format-arg-store
+  template<class Context, class... Args> struct format-arg-store;      // exposition only
+
+  template<class Context = format_context, class... Args>
+    format-arg-store<Context, Args...>
+      make_format_args(const Args&... args);
+  template<class... Args>
+    format-arg-store<wformat_context, Args...>
+      make_wformat_args(const Args&... args);
+
+  // [format.error], class format_error
+  class format_error;
+}
+
+namespace std {
+  template<class charT>
+  class basic_format_parse_context {
+  public:
+    using char_type = charT;
+    using const_iterator = typename basic_string_view<charT>::const_iterator;
+    using iterator = const_iterator;
+
+  private:
+    iterator begin_;                                    // exposition only
+    iterator end_;                                      // exposition only
+    enum indexing { unknown, manual, automatic };       // exposition only
+    indexing indexing_;                                 // exposition only
+    size_t next_arg_id_;                                // exposition only
+    size_t num_args_;                                   // exposition only
+
+  public:
+    constexpr explicit basic_format_parse_context(basic_string_view<charT> fmt,
+                                                  size_t num_args = 0) noexcept;
+    basic_format_parse_context(const basic_format_parse_context&) = delete;
+    basic_format_parse_context& operator=(const basic_format_parse_context&) = delete;
+
+    constexpr const_iterator begin() const noexcept;
+    constexpr const_iterator end() const noexcept;
+    constexpr void advance_to(const_iterator it);
+
+    constexpr size_t next_arg_id();
+    constexpr void check_arg_id(size_t id);
+  };
+}
+
+namespace std {
+  template<class Context>
+  class basic_format_arg {
+  public:
+    class handle;
+
+  private:
+    using char_type = typename Context::char_type;                              // exposition only
+
+    variant<monostate, bool, char_type,
+            int, unsigned int, long long int, unsigned long long int,
+            float, double, long double,
+            const char_type*, basic_string_view<char_type>,
+            const void*, handle> value;                                         // exposition only
+
+    template<class T> explicit basic_format_arg(const T& v) noexcept;           // exposition only
+    explicit basic_format_arg(float n) noexcept;                                // exposition only
+    explicit basic_format_arg(double n) noexcept;                               // exposition only
+    explicit basic_format_arg(long double n) noexcept;                          // exposition only
+    explicit basic_format_arg(const char_type* s);                              // exposition only
+
+    template<class traits>
+      explicit basic_format_arg(
+        basic_string_view<char_type, traits> s) noexcept;                       // exposition only
+
+    template<class traits, class Allocator>
+      explicit basic_format_arg(
+        const basic_string<char_type, traits, Allocator>& s) noexcept;          // exposition only
+
+    explicit basic_format_arg(nullptr_t) noexcept;                              // exposition only
+
+    template<class T>
+      explicit basic_format_arg(const T* p) noexcept;                           // exposition only
+
+  public:
+    basic_format_arg() noexcept;
+
+    explicit operator bool() const noexcept;
+  };
+}
+
+namespace std {
+  template<class Context, class... Args>
+  struct format-arg-store {      // exposition only
+    array<basic_format_arg<Context>, sizeof...(Args)> args;
+  };
+}
+
+namespace std {
+  class format_error : public runtime_error {
+  public:
+    explicit format_error(const string& what_arg);
+    explicit format_error(const char* what_arg);
+  };
+}
+*/
+
+#include <__config>
+#include <stdexcept>
+#include <version>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER > 17
+
+class _LIBCPP_EXCEPTION_ABI format_error : public runtime_error {
+public:
+  _LIBCPP_INLINE_VISIBILITY explicit format_error(const string& __s)
+      : runtime_error(__s) {}
+  _LIBCPP_INLINE_VISIBILITY explicit format_error(const char* __s)
+      : runtime_error(__s) {}
+  virtual ~format_error() noexcept;
+};
+
+#endif //_LIBCPP_STD_VER > 17
+
+_LIBCPP_END_NAMESPACE_STD
+
+_LIBCPP_POP_MACROS
+
+#endif // _LIBCPP_FORMAT
diff --git a/libcxx/include/module.modulemap b/libcxx/include/module.modulemap
--- a/libcxx/include/module.modulemap
+++ b/libcxx/include/module.modulemap
@@ -292,6 +292,10 @@
     header "filesystem"
     export *
   }
+  module format {
+    header "format"
+    export *
+  }
   module forward_list {
     header "forward_list"
     export initializer_list
diff --git a/libcxx/include/version b/libcxx/include/version
--- a/libcxx/include/version
+++ b/libcxx/include/version
@@ -59,6 +59,7 @@
 __cpp_lib_exchange_function                             201304L <utility>
 __cpp_lib_execution                                     201603L <execution>
 __cpp_lib_filesystem                                    201703L <filesystem>
+__cpp_lib_format                                        201907L <format>
 __cpp_lib_gcd_lcm                                       201606L <numeric>
 __cpp_lib_generic_associative_lookup                    201304L <map> <set>
 __cpp_lib_generic_unordered_lookup                      201811L <unordered_map> <unordered_set>
@@ -261,6 +262,7 @@
 # endif
 # define __cpp_lib_endian                               201907L
 # define __cpp_lib_erase_if                             202002L
+// # define __cpp_lib_format                               201907L
 # define __cpp_lib_generic_unordered_lookup             201811L
 # define __cpp_lib_int_pow2                             202002L
 # define __cpp_lib_interpolate                          201902L
diff --git a/libcxx/lib/abi/x86_64-unknown-linux-gnu.v1.abilist b/libcxx/lib/abi/x86_64-unknown-linux-gnu.v1.abilist
--- a/libcxx/lib/abi/x86_64-unknown-linux-gnu.v1.abilist
+++ b/libcxx/lib/abi/x86_64-unknown-linux-gnu.v1.abilist
@@ -712,6 +712,9 @@
 {'is_defined': True, 'name': '_ZNSt3__112ctype_bynameIwED0Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__112ctype_bynameIwED1Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__112ctype_bynameIwED2Ev', 'type': 'FUNC'}
+{'is_defined': True, 'name': '_ZNSt3__112format_errorD0Ev', 'type': 'FUNC'}
+{'is_defined': True, 'name': '_ZNSt3__112format_errorD1Ev', 'type': 'FUNC'}
+{'is_defined': True, 'name': '_ZNSt3__112format_errorD2Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__112future_errorC1ENS_10error_codeE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__112future_errorC2ENS_10error_codeE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__112future_errorD0Ev', 'type': 'FUNC'}
@@ -1620,6 +1623,7 @@
 {'is_defined': True, 'name': '_ZTINSt3__112codecvt_baseE', 'size': 16, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZTINSt3__112ctype_bynameIcEE', 'size': 24, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZTINSt3__112ctype_bynameIwEE', 'size': 24, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZTINSt3__112format_errorE', 'size': 24, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZTINSt3__112future_errorE', 'size': 24, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZTINSt3__112strstreambufE', 'size': 24, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZTINSt3__112system_errorE', 'size': 24, 'type': 'OBJECT'}
@@ -1744,6 +1748,7 @@
 {'is_defined': True, 'name': '_ZTSNSt3__112codecvt_baseE', 'size': 23, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZTSNSt3__112ctype_bynameIcEE', 'size': 26, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZTSNSt3__112ctype_bynameIwEE', 'size': 26, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZTSNSt3__112format_errorE', 'size': 23, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZTSNSt3__112future_errorE', 'size': 23, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZTSNSt3__112strstreambufE', 'size': 23, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZTSNSt3__112system_errorE', 'size': 23, 'type': 'OBJECT'}
@@ -1872,6 +1877,7 @@
 {'is_defined': True, 'name': '_ZTVNSt3__112bad_weak_ptrE', 'size': 40, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZTVNSt3__112ctype_bynameIcEE', 'size': 104, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZTVNSt3__112ctype_bynameIwEE', 'size': 136, 'type': 'OBJECT'}
+{'is_defined': True, 'name': '_ZTVNSt3__112format_errorE', 'size': 40, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZTVNSt3__112future_errorE', 'size': 40, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZTVNSt3__112strstreambufE', 'size': 128, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZTVNSt3__112system_errorE', 'size': 40, 'type': 'OBJECT'}
diff --git a/libcxx/src/CMakeLists.txt b/libcxx/src/CMakeLists.txt
--- a/libcxx/src/CMakeLists.txt
+++ b/libcxx/src/CMakeLists.txt
@@ -12,6 +12,7 @@
   condition_variable.cpp
   condition_variable_destructor.cpp
   exception.cpp
+  format.cpp
   functional.cpp
   future.cpp
   hash.cpp
diff --git a/libcxx/src/format.cpp b/libcxx/src/format.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/src/format.cpp
@@ -0,0 +1,19 @@
+//===------------------------- format.cpp ---------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "format"
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER > 17
+
+format_error::~format_error() noexcept = default;
+
+#endif //_LIBCPP_STD_VER > 17
+
+_LIBCPP_END_NAMESPACE_STD
diff --git a/libcxx/test/libcxx/double_include.sh.cpp b/libcxx/test/libcxx/double_include.sh.cpp
--- a/libcxx/test/libcxx/double_include.sh.cpp
+++ b/libcxx/test/libcxx/double_include.sh.cpp
@@ -75,6 +75,7 @@
 #include <filesystem>
 #include <float.h>
 #include <forward_list>
+#include <format>
 #include <functional>
 #ifndef _LIBCPP_HAS_NO_THREADS
 #include <future>
diff --git a/libcxx/test/std/language.support/support.limits/support.limits.general/format.version.pass.cpp b/libcxx/test/std/language.support/support.limits/support.limits.general/format.version.pass.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/std/language.support/support.limits/support.limits.general/format.version.pass.cpp
@@ -0,0 +1,58 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// WARNING: This test was generated by generate_feature_test_macro_components.py
+// and should not be edited manually.
+
+// <format>
+
+// Test the feature test macros defined by <format>
+
+/*  Constant            Value
+    __cpp_lib_format    201907L [C++2a]
+*/
+
+#include <format>
+#include "test_macros.h"
+
+#if TEST_STD_VER < 14
+
+# ifdef __cpp_lib_format
+#   error "__cpp_lib_format should not be defined before c++2a"
+# endif
+
+#elif TEST_STD_VER == 14
+
+# ifdef __cpp_lib_format
+#   error "__cpp_lib_format should not be defined before c++2a"
+# endif
+
+#elif TEST_STD_VER == 17
+
+# ifdef __cpp_lib_format
+#   error "__cpp_lib_format should not be defined before c++2a"
+# endif
+
+#elif TEST_STD_VER > 17
+
+# if !defined(_LIBCPP_VERSION)
+#   ifndef __cpp_lib_format
+#     error "__cpp_lib_format should be defined in c++2a"
+#   endif
+#   if __cpp_lib_format != 201907L
+#     error "__cpp_lib_format should have the value 201907L in c++2a"
+#   endif
+# else // _LIBCPP_VERSION
+#   ifdef __cpp_lib_format
+#     error "__cpp_lib_format should not be defined because it is unimplemented in libc++!"
+#   endif
+# endif
+
+#endif // TEST_STD_VER > 17
+
+int main(int, char**) { return 0; }
diff --git a/libcxx/test/std/language.support/support.limits/support.limits.general/version.version.pass.cpp b/libcxx/test/std/language.support/support.limits/support.limits.general/version.version.pass.cpp
--- a/libcxx/test/std/language.support/support.limits/support.limits.general/version.version.pass.cpp
+++ b/libcxx/test/std/language.support/support.limits/support.limits.general/version.version.pass.cpp
@@ -51,6 +51,7 @@
     __cpp_lib_exchange_function                    201304L [C++14]
     __cpp_lib_execution                            201603L [C++17]
     __cpp_lib_filesystem                           201703L [C++17]
+    __cpp_lib_format                               201907L [C++2a]
     __cpp_lib_gcd_lcm                              201606L [C++17]
     __cpp_lib_generic_associative_lookup           201304L [C++14]
     __cpp_lib_generic_unordered_lookup             201811L [C++2a]
@@ -263,6 +264,10 @@
 #   error "__cpp_lib_filesystem should not be defined before c++17"
 # endif
 
+# ifdef __cpp_lib_format
+#   error "__cpp_lib_format should not be defined before c++2a"
+# endif
+
 # ifdef __cpp_lib_gcd_lcm
 #   error "__cpp_lib_gcd_lcm should not be defined before c++17"
 # endif
@@ -658,6 +663,10 @@
 #   error "__cpp_lib_filesystem should not be defined before c++17"
 # endif
 
+# ifdef __cpp_lib_format
+#   error "__cpp_lib_format should not be defined before c++2a"
+# endif
+
 # ifdef __cpp_lib_gcd_lcm
 #   error "__cpp_lib_gcd_lcm should not be defined before c++17"
 # endif
@@ -1179,6 +1188,10 @@
 #   error "__cpp_lib_filesystem should have the value 201703L in c++17"
 # endif
 
+# ifdef __cpp_lib_format
+#   error "__cpp_lib_format should not be defined before c++2a"
+# endif
+
 # ifndef __cpp_lib_gcd_lcm
 #   error "__cpp_lib_gcd_lcm should be defined in c++17"
 # endif
@@ -1991,6 +2004,19 @@
 #   error "__cpp_lib_filesystem should have the value 201703L in c++2a"
 # endif
 
+# if !defined(_LIBCPP_VERSION)
+#   ifndef __cpp_lib_format
+#     error "__cpp_lib_format should be defined in c++2a"
+#   endif
+#   if __cpp_lib_format != 201907L
+#     error "__cpp_lib_format should have the value 201907L in c++2a"
+#   endif
+# else // _LIBCPP_VERSION
+#   ifdef __cpp_lib_format
+#     error "__cpp_lib_format should not be defined because it is unimplemented in libc++!"
+#   endif
+# endif
+
 # ifndef __cpp_lib_gcd_lcm
 #   error "__cpp_lib_gcd_lcm should be defined in c++2a"
 # endif
diff --git a/libcxx/test/std/utilities/format/format.error/format.error.pass.cpp b/libcxx/test/std/utilities/format/format.error/format.error.pass.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/std/utilities/format/format.error/format.error.pass.cpp
@@ -0,0 +1,56 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+
+// This test requires the dylib support introduced in D92214.
+// XFAIL: with_system_cxx_lib=macosx10.15
+// XFAIL: with_system_cxx_lib=macosx10.14
+// XFAIL: with_system_cxx_lib=macosx10.13
+// XFAIL: with_system_cxx_lib=macosx10.12
+// XFAIL: with_system_cxx_lib=macosx10.11
+// XFAIL: with_system_cxx_lib=macosx10.10
+// XFAIL: with_system_cxx_lib=macosx10.9
+
+// <format>
+
+// class format_error;
+
+#include <format>
+#include <type_traits>
+#include <cstring>
+#include <string>
+#include <cassert>
+
+#include "test_macros.h"
+
+int main(int, char**) {
+  static_assert(std::is_base_of_v<std::runtime_error, std::format_error>);
+  static_assert(std::is_polymorphic_v<std::format_error>);
+
+  {
+    const char* msg = "format_error message c-string";
+    std::format_error e(msg);
+    assert(std::strcmp(e.what(), msg) == 0);
+    std::format_error e2(e);
+    assert(std::strcmp(e2.what(), msg) == 0);
+    e2 = e;
+    assert(std::strcmp(e2.what(), msg) == 0);
+  }
+  {
+    std::string msg("format_error message std::string");
+    std::format_error e(msg);
+    assert(e.what() == msg);
+    std::format_error e2(e);
+    assert(e2.what() == msg);
+    e2 = e;
+    assert(e2.what() == msg);
+  }
+
+  return 0;
+}
diff --git a/libcxx/test/std/utilities/format/version.compile.pass.cpp b/libcxx/test/std/utilities/format/version.compile.pass.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/std/utilities/format/version.compile.pass.cpp
@@ -0,0 +1,20 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// <format>
+
+#include <format>
+
+#include "test_macros.h"
+
+#ifndef _LIBCPP_VERSION
+#  error _LIBCPP_VERSION not defined
+#endif
+
+// Required for MSVC internal test runner compatibility.
+int main(int, char**) { return 0; }
diff --git a/libcxx/utils/generate_feature_test_macro_components.py b/libcxx/utils/generate_feature_test_macro_components.py
--- a/libcxx/utils/generate_feature_test_macro_components.py
+++ b/libcxx/utils/generate_feature_test_macro_components.py
@@ -483,6 +483,11 @@
     "name": "__cpp_lib_constexpr_dynamic_alloc",
     "values": { "c++2a": int(201907) },
     "headers": ["memory"]
+   }, {
+    "name": "__cpp_lib_format",
+    "values": { "c++2a": int(201907) },
+    "headers": ["format"],
+    "unimplemented": True
    },
 ]], key=lambda tc: tc["name"])