Index: include/__config
===================================================================
--- include/__config
+++ include/__config
@@ -892,6 +892,8 @@
     defined(__CloudABI__) || \
     defined(__sun__)
 #  define _LIBCPP_HAS_THREAD_API_PTHREAD
+# elif defined(_WIN32)
+#  define _LIBCPP_HAS_THREAD_API_WIN32
 # else
 #  error "No thread API"
 # endif // _LIBCPP_HAS_THREAD_API
Index: include/__threading_support
===================================================================
--- include/__threading_support
+++ include/__threading_support
@@ -43,10 +43,21 @@
 #include <__external_threading>
 #else
 
+#if !defined(_LIBCPP_HAS_THREAD_API_PTHREAD) &&                                \
+    !defined(_LIBCPP_HAS_THREAD_API_EXTERNAL_PTHREAD) &&                       \
+    !defined(_LIBCPP_HAS_THREAD_API_WIN32)
+#error "unknown threading model"
+#endif
+
 #if defined(_LIBCPP_HAS_THREAD_API_PTHREAD) || \
     defined(_LIBCPP_HAS_THREAD_API_EXTERNAL_PTHREAD)
 #include <pthread.h>
 #include <sched.h>
+#elif defined(_LIBCPP_HAS_THREAD_API_WIN32)
+#define WIN32_LEAN_AND_MEAN
+#include <Windows.h>
+#include <process.h>
+#include <fibersapi.h>
 #endif
 
 #if defined(_LIBCPP_HAS_THREAD_API_EXTERNAL)
@@ -81,6 +92,29 @@
 
 // Thrad Local Storage
 typedef pthread_key_t __libcpp_tls_key;
+#elif defined(_LIBCPP_HAS_THREAD_API_WIN32)
+// Mutex
+typedef SRWLOCK __libcpp_mutex_t;
+#define _LIBCPP_MUTEX_INITIALIZER SRWLOCK_INIT
+
+typedef CRITICAL_SECTION __libcpp_recursive_mutex_t;
+
+// Condition Variable
+typedef CONDITION_VARIABLE __libcpp_condvar_t;
+#define _LIBCPP_CONDVAR_INITIALIZER CONDITION_VARIABLE_INIT
+
+// Execute once
+typedef INIT_ONCE __libcpp_exec_once_flag;
+#define _LIBCPP_EXEC_ONCE_INITIALIZER INIT_ONCE_STATIC_INIT
+
+// Thread ID
+typedef DWORD __libcpp_thread_id;
+
+// Thread
+typedef HANDLE __libcpp_thread_t;
+
+// Thread Local Storage
+typedef DWORD __libcpp_tls_key;
 #endif
 
 struct __libcpp_mutex_reference {
@@ -347,6 +381,236 @@
     return pthread_setspecific(__key, __p);
 }
 
+#elif defined(_LIBCPP_HAS_THREAD_API_WIN32)
+
+// Mutex
+_LIBCPP_ALWAYS_INLINE
+int __libcpp_recursive_mutex_init(__libcpp_recursive_mutex_t* __m)
+{
+  InitializeCriticalSection(__m);
+  return 0;
+}
+
+_LIBCPP_ALWAYS_INLINE
+int __libcpp_mutex_lock(__libcpp_mutex_reference&& __m)
+{
+  if (__m.__recursive)
+    EnterCriticalSection(__m);
+  else
+    AcquireSRWLockExclusive(__m);
+  return 0;
+}
+
+_LIBCPP_ALWAYS_INLINE
+int __libcpp_mutex_trylock(__libcpp_mutex_reference&& __m)
+{
+  if (__m.__recursive)
+    return TryEnterCriticalSection(__m);
+  return TryAcquireSRWLockExclusive(__m);
+}
+
+_LIBCPP_ALWAYS_INLINE
+int __libcpp_mutex_unlock(__libcpp_mutex_reference&& __m)
+{
+  if (__m.__recursive)
+    LeaveCriticalSection(__m);
+  else
+    ReleaseSRWLockExclusive(__m);
+  return 0;
+}
+
+_LIBCPP_ALWAYS_INLINE
+int __libcpp_mutex_destroy(__libcpp_mutex_reference&& __m)
+{
+  static_cast<void>(__m);
+  return 0;
+}
+
+// Condition Variable
+_LIBCPP_ALWAYS_INLINE
+int __libcpp_condvar_signal(__libcpp_condvar_t* __cv)
+{
+  WakeConditionVariable(__cv);
+  return 0;
+}
+
+_LIBCPP_ALWAYS_INLINE
+int __libcpp_condvar_broadcast(__libcpp_condvar_t* __cv)
+{
+  WakeAllConditionVariable(__cv);
+  return 0;
+}
+
+_LIBCPP_ALWAYS_INLINE
+int __libcpp_condvar_wait(__libcpp_condvar_t* __cv,
+                          __libcpp_mutex_reference&& __m)
+{
+  if (__m.__recursive)
+    SleepConditionVariableCS(__cv, __m, INFINITE);
+  else
+    SleepConditionVariableSRW(__cv, __m, INFINITE, 0);
+  return 0;
+}
+
+_LIBCPP_ALWAYS_INLINE
+int __libcpp_condvar_timedwait(__libcpp_condvar_t* __cv,
+                               __libcpp_mutex_reference&& __m,
+                               timespec* __ts)
+{
+  using namespace _VSTD::chrono;
+  auto timeout = seconds(__ts->tv_sec) + nanoseconds(__ts->tv_nsec);
+  auto timeout_ms = duration_cast<milliseconds>(timeout);
+
+  _LIBCPP_ASSERT(timeout_ms.count() < _VSTD::numeric_limits<DWORD>::max(),
+                 "timeout duration overflows");
+
+  if (__m.__recursive) {
+    if (!SleepConditionVariableCS(__cv, __m, timeout_ms.count()))
+      return GetLastError();
+  } else {
+    if (!SleepConditionVariableSRW(__cv, __m, timeout_ms.count(), 0))
+      return GetLastError();
+  }
+  return 0;
+}
+
+_LIBCPP_ALWAYS_INLINE
+int __libcpp_condvar_destroy(__libcpp_condvar_t* __cv)
+{
+  static_cast<void>(__cv);
+  return 0;
+}
+
+// Execute once
+static inline _LIBCPP_ALWAYS_INLINE BOOL CALLBACK
+__libcpp_init_once_trampoline(PINIT_ONCE InitOnce, PVOID Parameter,
+                              PVOID *Context)
+{
+  static_cast<void>(InitOnce);
+  static_cast<void>(Context);
+
+  void (*init_routine)(void) = reinterpret_cast<void (*)(void)>(Parameter);
+  init_routine();
+  return TRUE;
+}
+
+int __libcpp_execute_once(__libcpp_exec_once_flag* flag,
+                          void (*init_routine)(void))
+{
+  if (!InitOnceExecuteOnce(flag, __libcpp_init_once_trampoline,
+                           reinterpret_cast<void*>(init_routine), NULL))
+    return GetLastError();
+  return 0;
+}
+
+// Thread ID
+_LIBCPP_ALWAYS_INLINE
+bool __libcpp_thread_id_equal(__libcpp_thread_id __lhs,
+                              __libcpp_thread_id __rhs)
+{
+  return __lhs == __rhs;
+}
+
+_LIBCPP_ALWAYS_INLINE
+bool __libcpp_thread_id_less(__libcpp_thread_id __lhs, __libcpp_thread_id __rhs)
+{
+  return __lhs < __rhs;
+}
+
+struct __libcpp_thread_trampoline_data
+{
+  void* (*__func)(void*);
+  void* __arg;
+};
+
+static inline _LIBCPP_ALWAYS_INLINE unsigned int WINAPI
+__libcpp_thread_trampoline(void *__data)
+{
+  __libcpp_thread_trampoline_data data =
+      *(__libcpp_thread_trampoline_data*)__data;
+  _VSTD::free(__data);
+  return reinterpret_cast<unsigned int>(data.__func(data.__arg));
+}
+
+// Thread
+_LIBCPP_ALWAYS_INLINE
+int __libcpp_thread_create(__libcpp_thread_t* __t, void* (*__func)(void*),
+                           void* __arg)
+{
+  __libcpp_thread_trampoline_data* data =
+      reinterpret_cast<__libcpp_thread_trampoline_data*>(_VSTD::malloc(sizeof(*data)));
+  data->__func = __func;
+  data->__arg = __arg;
+
+  *__t = reinterpret_cast<HANDLE>(_beginthreadex(NULL, 0,
+                                                 __libcpp_thread_trampoline,
+                                                 data, 0, NULL));
+  if (*__t)
+    return 0;
+  return GetLastError();
+}
+
+_LIBCPP_ALWAYS_INLINE
+__libcpp_thread_id __libcpp_thread_get_current_id()
+{
+  return GetCurrentThreadId();
+}
+
+_LIBCPP_ALWAYS_INLINE
+__libcpp_thread_id __libcpp_thread_get_id(const __libcpp_thread_t* __t)
+{
+  return GetThreadId(*__t);
+}
+
+_LIBCPP_ALWAYS_INLINE
+int __libcpp_thread_join(__libcpp_thread_t* __t)
+{
+  if (WaitForSingleObjectEx(*__t, INFINITE, FALSE) == WAIT_FAILED)
+    return GetLastError();
+  if (!CloseHandle(*__t))
+    return GetLastError();
+  return 0;
+}
+
+_LIBCPP_ALWAYS_INLINE
+int __libcpp_thread_detach(__libcpp_thread_t* __t)
+{
+  if (!CloseHandle(*__t))
+    return GetLastError();
+  return 0;
+}
+
+_LIBCPP_ALWAYS_INLINE
+void __libcpp_thread_yield()
+{
+  SwitchToThread();
+}
+
+// Thread Local Storage
+_LIBCPP_ALWAYS_INLINE
+int __libcpp_tls_create(__libcpp_tls_key* __key, void (*__at_exit)(void*))
+{
+  // TODO(compnerd) provide a wrapper for CC adjustment
+  *__key = FlsAlloc(reinterpret_cast<void(WINAPI*)(void*)>(__at_exit));
+  if (*__key == FLS_OUT_OF_INDEXES)
+    return GetLastError();
+  return 0;
+}
+
+_LIBCPP_ALWAYS_INLINE
+void* __libcpp_tls_get(__libcpp_tls_key __key)
+{
+  return FlsGetValue(__key);
+}
+
+_LIBCPP_ALWAYS_INLINE
+int __libcpp_tls_set(__libcpp_tls_key __key, void* __p)
+{
+  if (!FlsSetValue(__key, __p))
+    return GetLastError();
+  return 0;
+}
+
 #endif // _LIBCPP_HAS_THREAD_API_PTHREAD
 
 _LIBCPP_END_NAMESPACE_STD