Index: libcxx/include/filesystem
===================================================================
--- libcxx/include/filesystem
+++ libcxx/include/filesystem
@@ -568,9 +568,21 @@
 template <class _ECharT>
 typename enable_if<__can_convert_char<_ECharT>::value, bool>::type
 __is_separator(_ECharT __e) {
+#if defined(_LIBCPP_WIN32API)
+  return __e == _ECharT('/') || __e == _ECharT('\\');
+#else
   return __e == _ECharT('/');
+#endif
 }
 
+#ifndef _LIBCPP_NO_HAS_CHAR8_T
+typedef char8_t __u8_value;
+typedef u8string __u8_string;
+#else
+typedef char __u8_value;
+typedef string __u8_string;
+#endif
+
 struct _NullSentinel {};
 
 template <class _Tp>
@@ -672,6 +684,14 @@
 template <class _Tp>
 struct __is_pathable<_Tp, false, false, true> : __is_pathable_iter<_Tp> {};
 
+#if defined(_LIBCPP_WIN32API)
+typedef wstring __path_string;
+typedef wchar_t __path_value;
+#else
+typedef string __path_string;
+typedef char __path_value;
+#endif
+
 template <class _ECharT>
 struct _PathCVT;
 
@@ -682,24 +702,40 @@
                 "Char type not convertible");
 
   typedef __narrow_to_utf8<sizeof(_ECharT) * __CHAR_BIT__> _Narrower;
+#if defined(_LIBCPP_WIN32API)
+  typedef __widen_from_utf8<sizeof(wchar_t) * __CHAR_BIT__> _Widener;
+#endif
 
-  static void __append_range(string& __dest, _ECharT const* __b,
+  static void __append_range(__path_string& __dest, _ECharT const* __b,
                              _ECharT const* __e) {
+#if defined(_LIBCPP_WIN32API)
+    string __utf8;
+    _Narrower()(back_inserter(__utf8), __b, __e);
+    _Widener()(back_inserter(__dest), __utf8.data(), __utf8.data() + __utf8.size());
+#else
     _Narrower()(back_inserter(__dest), __b, __e);
+#endif
   }
 
   template <class _Iter>
-  static void __append_range(string& __dest, _Iter __b, _Iter __e) {
+  static void __append_range(__path_string& __dest, _Iter __b, _Iter __e) {
     static_assert(!is_same<_Iter, _ECharT*>::value, "Call const overload");
     if (__b == __e)
       return;
     basic_string<_ECharT> __tmp(__b, __e);
+#if defined(_LIBCPP_WIN32API)
+    string __utf8;
+    _Narrower()(back_inserter(__utf8), __tmp.data(),
+                __tmp.data() + __tmp.length());
+    _Widener()(back_inserter(__dest), __utf8.data(), __utf8.data() + __utf8.size());
+#else
     _Narrower()(back_inserter(__dest), __tmp.data(),
                 __tmp.data() + __tmp.length());
+#endif
   }
 
   template <class _Iter>
-  static void __append_range(string& __dest, _Iter __b, _NullSentinel) {
+  static void __append_range(__path_string& __dest, _Iter __b, _NullSentinel) {
     static_assert(!is_same<_Iter, _ECharT*>::value, "Call const overload");
     const _ECharT __sentinel = _ECharT{};
     if (*__b == __sentinel)
@@ -707,12 +743,19 @@
     basic_string<_ECharT> __tmp;
     for (; *__b != __sentinel; ++__b)
       __tmp.push_back(*__b);
+#if defined(_LIBCPP_WIN32API)
+    string __utf8;
+    _Narrower()(back_inserter(__utf8), __tmp.data(),
+                __tmp.data() + __tmp.length());
+    _Widener()(back_inserter(__dest), __utf8.data(), __utf8.data() + __utf8.size());
+#else
     _Narrower()(back_inserter(__dest), __tmp.data(),
                 __tmp.data() + __tmp.length());
+#endif
   }
 
   template <class _Source>
-  static void __append_source(string& __dest, _Source const& __s) {
+  static void __append_source(__path_string& __dest, _Source const& __s) {
     using _Traits = __is_pathable<_Source>;
     __append_range(__dest, _Traits::__range_begin(__s),
                    _Traits::__range_end(__s));
@@ -721,36 +764,79 @@
 #endif // !_LIBCPP_HAS_NO_LOCALIZATION
 
 template <>
-struct _PathCVT<char> {
+struct _PathCVT<__path_value> {
 
   template <class _Iter>
   static typename enable_if<__is_exactly_cpp17_input_iterator<_Iter>::value>::type
-  __append_range(string& __dest, _Iter __b, _Iter __e) {
+  __append_range(__path_string& __dest, _Iter __b, _Iter __e) {
     for (; __b != __e; ++__b)
       __dest.push_back(*__b);
   }
 
   template <class _Iter>
   static typename enable_if<__is_cpp17_forward_iterator<_Iter>::value>::type
-  __append_range(string& __dest, _Iter __b, _Iter __e) {
+  __append_range(__path_string& __dest, _Iter __b, _Iter __e) {
     __dest.__append_forward_unsafe(__b, __e);
   }
 
   template <class _Iter>
-  static void __append_range(string& __dest, _Iter __b, _NullSentinel) {
+  static void __append_range(__path_string& __dest, _Iter __b, _NullSentinel) {
     const char __sentinel = char{};
     for (; *__b != __sentinel; ++__b)
       __dest.push_back(*__b);
   }
 
   template <class _Source>
-  static void __append_source(string& __dest, _Source const& __s) {
+  static void __append_source(__path_string& __dest, _Source const& __s) {
     using _Traits = __is_pathable<_Source>;
     __append_range(__dest, _Traits::__range_begin(__s),
                    _Traits::__range_end(__s));
   }
 };
 
+#if defined(_LIBCPP_WIN32API)
+template <class _ECharT>
+struct _PathExport {
+  typedef __narrow_to_utf8<sizeof(wchar_t) * __CHAR_BIT__> _Narrower;
+  typedef __widen_from_utf8<sizeof(_ECharT) * __CHAR_BIT__> _Widener;
+
+  template <class _Str>
+  static void __append(_Str& __dest, const __path_string& __src) {
+    string __utf8;
+    _Narrower()(back_inserter(__utf8), __src.data(), __src.data() + __src.size());
+    _Widener()(back_inserter(__dest), __utf8.data(), __utf8.data() + __utf8.size());
+  }
+};
+
+template <>
+struct _PathExport<wchar_t> {
+  template <class _Str>
+  static void __append(_Str& __dest, const __path_string& __src) {
+    __dest.append(__src.begin(), __src.end());
+  }
+};
+
+template <>
+struct _PathExport<char16_t> {
+  template <class _Str>
+  static void __append(_Str& __dest, const __path_string& __src) {
+    __dest.append(__src.begin(), __src.end());
+  }
+};
+
+#ifndef _LIBCPP_NO_HAS_CHAR8_T
+template <>
+struct _PathExport<char8_t> {
+  typedef __narrow_to_utf8<sizeof(wchar_t) * __CHAR_BIT__> _Narrower;
+
+  template <class _Str>
+  static void __append(_Str& __dest, const __path_string& __src) {
+    _Narrower()(back_inserter(__dest), __src.data(), __src.data() + __src.size());
+  }
+};
+#endif
+#endif
+
 class _LIBCPP_TYPE_VIS path {
   template <class _SourceOrIter, class _Tp = path&>
   using _EnableIfPathable =
@@ -763,10 +849,15 @@
   using _SourceCVT = _PathCVT<_SourceChar<_Tp> >;
 
 public:
+#if defined(_LIBCPP_WIN32API)
+  typedef wchar_t value_type;
+  static constexpr value_type preferred_separator = '\\';
+#else
   typedef char value_type;
-  typedef basic_string<value_type> string_type;
-  typedef _VSTD::string_view __string_view;
   static constexpr value_type preferred_separator = '/';
+#endif
+  typedef basic_string<value_type> string_type;
+  typedef basic_string_view<value_type> __string_view;
 
   enum class _LIBCPP_ENUM_VIS format : unsigned char {
     auto_format,
@@ -1001,6 +1092,52 @@
 
   _LIBCPP_INLINE_VISIBILITY operator string_type() const { return __pn_; }
 
+#if defined(_LIBCPP_WIN32API)
+  _LIBCPP_INLINE_VISIBILITY std::wstring wstring() const { return __pn_; }
+
+  std::wstring generic_wstring() const { return __pn_; }
+
+#if !defined(_LIBCPP_HAS_NO_LOCALIZATION)
+  template <class _ECharT, class _Traits = char_traits<_ECharT>,
+            class _Allocator = allocator<_ECharT> >
+  basic_string<_ECharT, _Traits, _Allocator>
+  string(const _Allocator& __a = _Allocator()) const {
+    using _Str = basic_string<_ECharT, _Traits, _Allocator>;
+    _Str __s(__a);
+    __s.reserve(__pn_.size());
+    _PathExport<_ECharT>::__append(__s, __pn_);
+    return __s;
+  }
+
+  _LIBCPP_INLINE_VISIBILITY std::string string() const {
+    return string<char>();
+  }
+  _LIBCPP_INLINE_VISIBILITY __u8_string u8string() const {
+    return string<__u8_value>();
+  }
+
+  _LIBCPP_INLINE_VISIBILITY std::u16string u16string() const {
+    return string<char16_t>();
+  }
+  _LIBCPP_INLINE_VISIBILITY std::u32string u32string() const {
+    return string<char32_t>();
+  }
+
+  // generic format observers
+  template <class _ECharT, class _Traits = char_traits<_ECharT>,
+            class _Allocator = allocator<_ECharT> >
+  basic_string<_ECharT, _Traits, _Allocator>
+  generic_string(const _Allocator& __a = _Allocator()) const {
+    return string<_ECharT, _Traits, _Allocator>(__a);
+  }
+
+  std::string generic_string() const { return generic_string<char>(); }
+  std::u16string generic_u16string() const { return generic_string<char16_t>(); }
+  std::u32string generic_u32string() const { return generic_string<char32_t>(); }
+  __u8_string generic_u8string() const { return u8string(); }
+#endif /* !_LIBCPP_HAS_NO_LOCALIZATION */
+#else /* !_WIN32 */
+
   _LIBCPP_INLINE_VISIBILITY std::string string() const { return __pn_; }
 #ifndef _LIBCPP_NO_HAS_CHAR8_T
   _LIBCPP_INLINE_VISIBILITY std::u8string u8string() const { return std::u8string(__pn_.begin(), __pn_.end()); }
@@ -1030,7 +1167,7 @@
   _LIBCPP_INLINE_VISIBILITY std::u32string u32string() const {
     return string<char32_t>();
   }
-#endif
+#endif /* !_LIBCPP_HAS_NO_LOCALIZATION */
 
   // generic format observers
   std::string generic_string() const { return __pn_; }
@@ -1051,7 +1188,8 @@
   std::wstring generic_wstring() const { return string<wchar_t>(); }
   std::u16string generic_u16string() const { return string<char16_t>(); }
   std::u32string generic_u32string() const { return string<char32_t>(); }
-#endif
+#endif /* !_LIBCPP_HAS_NO_LOCALIZATION */
+#endif /* !_LIBCPP_WIN32API */
 
 private:
   int __compare(__string_view) const;
@@ -1158,7 +1296,7 @@
 #if !defined(_LIBCPP_HAS_NO_LOCALIZATION)
   template <class _CharT, class _Traits>
   _LIBCPP_INLINE_VISIBILITY friend
-      typename enable_if<is_same<_CharT, char>::value &&
+      typename enable_if<is_same<_CharT, value_type>::value &&
                              is_same<_Traits, char_traits<char> >::value,
                          basic_ostream<_CharT, _Traits>&>::type
       operator<<(basic_ostream<_CharT, _Traits>& __os, const path& __p) {
@@ -1168,7 +1306,7 @@
 
   template <class _CharT, class _Traits>
   _LIBCPP_INLINE_VISIBILITY friend
-      typename enable_if<!is_same<_CharT, char>::value ||
+      typename enable_if<!is_same<_CharT, value_type>::value ||
                              !is_same<_Traits, char_traits<char> >::value,
                          basic_ostream<_CharT, _Traits>&>::type
       operator<<(basic_ostream<_CharT, _Traits>& __os, const path& __p) {
Index: libcxx/src/filesystem/filesystem_common.h
===================================================================
--- libcxx/src/filesystem/filesystem_common.h
+++ libcxx/src/filesystem/filesystem_common.h
@@ -38,6 +38,12 @@
 #pragma GCC diagnostic ignored "-Wunused-function"
 #endif
 
+#if defined(_LIBCPP_WIN32API)
+#define PS(x) (L##x)
+#else
+#define PS(x) (x)
+#endif
+
 _LIBCPP_BEGIN_NAMESPACE_FILESYSTEM
 
 namespace detail {
@@ -94,8 +100,8 @@
   return result;
 }
 
-const char* unwrap(string const& s) { return s.c_str(); }
-const char* unwrap(path const& p) { return p.native().c_str(); }
+const path::value_type* unwrap(path::string_type const& s) { return s.c_str(); }
+const path::value_type* unwrap(path const& p) { return p.native().c_str(); }
 template <class Arg>
 Arg const& unwrap(Arg const& a) {
   static_assert(!is_class<Arg>::value, "cannot pass class here");
Index: libcxx/src/filesystem/operations.cpp
===================================================================
--- libcxx/src/filesystem/operations.cpp
+++ libcxx/src/filesystem/operations.cpp
@@ -171,11 +171,11 @@
     switch (State) {
     case PS_BeforeBegin:
     case PS_AtEnd:
-      return "";
+      return PS("");
     case PS_InRootDir:
-      return "/";
+      return PS("/");
     case PS_InTrailingSep:
-      return "";
+      return PS("");
     case PS_InRootName:
     case PS_InFilenames:
       return RawEntry;
@@ -283,8 +283,8 @@
 };
 
 string_view_pair separate_filename(string_view_t const& s) {
-  if (s == "." || s == ".." || s.empty())
-    return string_view_pair{s, ""};
+  if (s == PS(".") || s == PS("..") || s.empty())
+    return string_view_pair{s, PS("")};
   auto pos = s.find_last_of('.');
   if (pos == string_view_t::npos || pos == 0)
     return string_view_pair{s, string_view_t{}};
@@ -495,19 +495,25 @@
 
 filesystem_error::~filesystem_error() {}
 
+#if defined(_LIBCPP_WIN32API)
+#define PS_FMT "%ls"
+#else
+#define PS_FMT "%s"
+#endif
+
 void filesystem_error::__create_what(int __num_paths) {
   const char* derived_what = system_error::what();
   __storage_->__what_ = [&]() -> string {
-    const char* p1 = path1().native().empty() ? "\"\"" : path1().c_str();
-    const char* p2 = path2().native().empty() ? "\"\"" : path2().c_str();
+    const path::value_type* p1 = path1().native().empty() ? PS("\"\"") : path1().c_str();
+    const path::value_type* p2 = path2().native().empty() ? PS("\"\"") : path2().c_str();
     switch (__num_paths) {
     default:
       return detail::format_string("filesystem error: %s", derived_what);
     case 1:
-      return detail::format_string("filesystem error: %s [%s]", derived_what,
+      return detail::format_string("filesystem error: %s [" PS_FMT "]", derived_what,
                                    p1);
     case 2:
-      return detail::format_string("filesystem error: %s [%s] [%s]",
+      return detail::format_string("filesystem error: %s [" PS_FMT "] [" PS_FMT "]",
                                    derived_what, p1, p2);
     }
   }();
@@ -1204,10 +1210,10 @@
   error_code m_ec;
   file_status st = detail::posix_stat(p, &m_ec);
   if (!status_known(st))
-    return err.report(m_ec, "cannot access path \"%s\"", p);
+    return err.report(m_ec, "cannot access path \"" PS_FMT "\"", p);
 
   if (!exists(st) || !is_directory(st))
-    return err.report(errc::not_a_directory, "path \"%s\" is not a directory",
+    return err.report(errc::not_a_directory, "path \"" PS_FMT "\" is not a directory",
                       p);
 
   return p;
@@ -1263,7 +1269,7 @@
   }
   if (!replacement.empty()) {
     if (replacement.native()[0] != '.') {
-      __pn_ += ".";
+      __pn_ += PS(".");
     }
     __pn_.append(replacement.__pn_);
   }
@@ -1385,11 +1391,11 @@
 static PathPartKind ClassifyPathPart(string_view_t Part) {
   if (Part.empty())
     return PK_TrailingSep;
-  if (Part == ".")
+  if (Part == PS("."))
     return PK_Dot;
-  if (Part == "..")
+  if (Part == PS(".."))
     return PK_DotDot;
-  if (Part == "/")
+  if (Part == PS("/"))
     return PK_RootSep;
   return PK_Filename;
 }
@@ -1438,7 +1444,7 @@
         NewPathSize -= Parts.back().first.size();
         Parts.pop_back();
       } else if (LastKind != PK_RootSep)
-        AddPart(PK_DotDot, "..");
+        AddPart(PK_DotDot, PS(".."));
       MaybeNeedTrailingSep = LastKind == PK_Filename;
       break;
     }
@@ -1453,7 +1459,7 @@
   }
   // [fs.path.generic]p6.8: If the path is empty, add a dot.
   if (Parts.empty())
-    return ".";
+    return PS(".");
 
   // [fs.path.generic]p6.7: If the last filename is dot-dot, remove any
   // trailing directory-separator.
@@ -1465,7 +1471,7 @@
     Result /= PK.first;
 
   if (NeedTrailingSep)
-    Result /= "";
+    Result /= PS("");
 
   return Result;
 }
@@ -1474,9 +1480,9 @@
   int Count = 0;
   for (; PP; ++PP) {
     auto Elem = *PP;
-    if (Elem == "..")
+    if (Elem == PS(".."))
       --Count;
-    else if (Elem != "." && Elem != "")
+    else if (Elem != PS(".") && Elem != PS(""))
       ++Count;
   }
   return Count;
@@ -1523,15 +1529,15 @@
     return {};
 
   // if n == 0 and (a == end() || a->empty()), returns path("."); otherwise
-  if (ElemCount == 0 && (PP.atEnd() || *PP == ""))
-    return ".";
+  if (ElemCount == 0 && (PP.atEnd() || *PP == PS("")))
+    return PS(".");
 
   // return a path constructed with 'n' dot-dot elements, followed by the the
   // elements of '*this' after the mismatch.
   path Result;
   // FIXME: Reserve enough room in Result that it won't have to re-allocate.
   while (ElemCount--)
-    Result /= "..";
+    Result /= PS("..");
   for (; PP; ++PP)
     Result /= *PP;
   return Result;
@@ -1544,7 +1550,7 @@
     return 0;
 
   auto GetRootName = [](PathParser *Parser) -> string_view_t {
-    return Parser->inRootName() ? **Parser : "";
+    return Parser->inRootName() ? **Parser : PS("");
   };
   int res = GetRootName(LHS).compare(GetRootName(RHS));
   ConsumeRootName(LHS);