diff --git a/docs/DesignDocs/DebugMode.rst b/docs/DesignDocs/DebugMode.rst
new file mode 100644
index 0000000..166c733
--- /dev/null
+++ b/docs/DesignDocs/DebugMode.rst
@@ -0,0 +1,100 @@
+==========
+Debug Mode
+==========
+
+.. contents::
+   :local
+
+.. _using-debug-mode:
+
+Using Debug Mode
+================
+
+Libc++ provides a debug mode that enables assertions meant to detect incorrect
+usage of the standard library. By default these assertions are disabled but
+they can be enabled using the ``_LIBCPP_DEBUG`` macro.
+
+**_LIBCPP_DEBUG** Macro
+-----------------------
+
+**_LIBCPP_DEBUG**:
+  This macro is used to enable assertions and iterator debugging checks within
+  libc++. By default it is undefined.
+
+  **Values**: ``0``, ``1``
+
+  Defining ``_LIBCPP_DEBUG`` to ``0`` or greater enables most of libc++'s
+  assertions. Defining ``_LIBCPP_DEBUG`` to ``1`` enables "iterator debugging"
+  which provides additional assertions about the validity of iterators used by
+  the program.
+
+  Note that this option has no effect on libc++'s ABI
+
+**_LIBCPP_DEBUG_USE_EXCEPTIONS**:
+  When this macro is defined ``_LIBCPP_ASSERT`` failures throw
+  ``__libcpp_debug_exception`` instead of aborting. Additionally this macro
+  disables exception specifications on functions containing ``_LIBCPP_ASSERT``
+  checks. This allows assertion failures to correctly throw through these
+  functions.
+
+Handling Assertion Failures
+---------------------------
+
+When a debug assertion fails the assertion handler is called via the
+``std::__libcpp_debug_function`` function pointer. It is possible to override
+this function pointer using a different handler function. Libc++ provides two
+different assertion handlers, the default handler
+``std::__libcpp_abort_debug_handler`` which aborts the program, and
+``std::__libcpp_throw_debug_handler`` which throws an instance of
+``std::__libcpp_debug_exception``. Libc++ can be changed to use the throwing
+assertion handler as follows:
+
+.. code-block:: cpp
+
+  #define _LIBCPP_DEBUG 1
+  #include <string>
+  int main() {
+    std::__libcpp_debug_function = std::__libcpp_throw_debug_function;
+    try {
+      std::string::iterator bad_it;
+      std::string str("hello world");
+      str.insert(bad_it, '!'); // causes debug assertion
+    } catch (std::__libcpp_debug_exception const&) {
+      return EXIT_SUCCESS;
+    }
+    return EXIT_FAILURE;
+  }
+
+Debug Mode Checks
+=================
+
+Libc++'s debug mode offers two levels of checking. The first enables various
+precondition checks throughout libc++. The second additionally enables
+"iterator debugging" which checks the validity of iterators used by the program.
+
+Basic Checks
+============
+
+These checks are enabled when ``_LIBCPP_DEBUG`` is defined to either 0 or 1.
+
+The following checks are enabled by ``_LIBCPP_DEBUG``:
+
+  * FIXME: Update this list
+
+Iterator Debugging Checks
+=========================
+
+These checks are enabled when ``_LIBCPP_DEBUG`` is defined to 1.
+
+The following containers and STL classes support iterator debugging:
+
+  * ``std::string``
+  * ``std::vector<T>`` (``T != bool``)
+  * ``std::list``
+  * ``std::unordered_map``
+  * ``std::unordered_multimap``
+  * ``std::unordered_set``
+  * ``std::unordered_multiset``
+
+The remaining containers do not currently support iterator debugging.
+Patches welcome.
diff --git a/docs/UsingLibcxx.rst b/docs/UsingLibcxx.rst
index d6d1095..de87c9c 100644
--- a/docs/UsingLibcxx.rst
+++ b/docs/UsingLibcxx.rst
@@ -133,17 +133,7 @@
 thread safety annotations.
 
 **_LIBCPP_DEBUG**:
-  This macro is used to enable assertions and other debugging checks within
-  libc++. All debugging checks are disabled by default.
-
-  **Values**: ``0``, ``1``
-
-  Defining ``_LIBCPP_DEBUG`` to ``0`` or greater enables most of libc++'s
-  assertions. Defining ``_LIBCPP_DEBUG`` to ``1`` enables "iterator debugging"
-  which provides additional assertions about the validity of iterators used by
-  the program.
-
-  Note that this option has no effect on libc++'s ABI
+  See :ref:`using-debug-mode` for more information.
 
 **_LIBCPP_ENABLE_THREAD_SAFETY_ANNOTATIONS**:
   This macro is used to enable -Wthread-safety annotations on libc++'s
diff --git a/docs/index.rst b/docs/index.rst
index 0cac7fe..c62dfe8 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -127,6 +127,7 @@
 .. toctree::
    :maxdepth: 1
 
+   DesignDocs/DebugMode
    DesignDocs/CapturingConfigInfo
    DesignDocs/ABIVersioning
    DesignDocs/VisibilityMacros
diff --git a/include/__config b/include/__config
index d6ab234..868914d 100644
--- a/include/__config
+++ b/include/__config
@@ -651,6 +651,17 @@
 #  define _NOEXCEPT_(x)
 #endif
 
+#if defined(_LIBCPP_DEBUG_USE_EXCEPTIONS)
+# if !defined(_LIBCPP_DEBUG)
+#   error cannot use _LIBCPP_DEBUG_USE_EXCEPTIONS unless _LIBCPP_DEBUG is defined
+# endif
+# define _NOEXCEPT_DEBUG noexcept(false)
+# define _NOEXCEPT_DEBUG_(x) noexcept(false)
+#else
+# define _NOEXCEPT_DEBUG _NOEXCEPT
+# define _NOEXCEPT_DEBUG_(x) _NOEXCEPT_(x)
+#endif
+
 #ifdef _LIBCPP_HAS_NO_UNICODE_CHARS
 typedef unsigned short char16_t;
 typedef unsigned int   char32_t;
diff --git a/include/__debug b/include/__debug
index e67dd08..e3a5ec9 100644
--- a/include/__debug
+++ b/include/__debug
@@ -17,13 +17,16 @@
 #pragma GCC system_header
 #endif
 
-#if _LIBCPP_DEBUG_LEVEL >= 1
+#if _LIBCPP_DEBUG_LEVEL >= 1 || defined(_LIBCPP_BUILDING_LIBRARY)
 #   include <cstdlib>
 #   include <cstdio>
 #   include <cstddef>
-#   ifndef _LIBCPP_ASSERT
-#      define _LIBCPP_ASSERT(x, m) ((x) ? (void)0 : (_VSTD::fprintf(stderr, "%s\n", m), _VSTD::abort()))
-#   endif
+#   include <exception>
+#endif
+
+#if _LIBCPP_DEBUG_LEVEL >= 1 && !defined(_LIBCPP_ASSERT)
+# define _LIBCPP_ASSERT(x, m) ((x) ? (void)0 : \
+  _VSTD::__libcpp_debug_function(_VSTD::__libcpp_debug_info{__FILE__, __LINE__, #x, m}))
 #endif
 
 #if _LIBCPP_DEBUG_LEVEL >= 2
@@ -43,10 +46,61 @@
 #define _LIBCPP_DEBUG_MODE(...) ((void)0)
 #endif
 
-#if _LIBCPP_DEBUG_LEVEL >= 2
+#if _LIBCPP_DEBUG_LEVEL < 1
+class _LIBCPP_EXCEPTION_ABI __libcpp_debug_exception;
+#endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
+struct _LIBCPP_TYPE_VIS_ONLY __libcpp_debug_info {
+  const char* __file_;
+  int __line_;
+  const char* __pred_;
+  const char* __msg_;
+};
+
+/// __libcpp_debug_function_type - The type of the assertion failure handler.
+typedef void(*__libcpp_debug_function_type)(__libcpp_debug_info const&);
+
+/// __libcpp_debug_function - The handler function called when a _LIBCPP_ASSERT
+///    fails.
+extern __libcpp_debug_function_type __libcpp_debug_function;
+
+/// __libcpp_abort_debug_function - A debug handler that aborts when called.
+_LIBCPP_NORETURN _LIBCPP_FUNC_VIS
+void __libcpp_abort_debug_function(__libcpp_debug_info const&);
+
+/// __libcpp_throw_debug_function - A debug handler that throws
+///   an instance of __libcpp_debug_exception when called.
+ _LIBCPP_NORETURN _LIBCPP_FUNC_VIS
+void __libcpp_throw_debug_function(__libcpp_debug_info const&);
+
+/// __libcpp_set_debug_function - Set the debug handler to the specified
+///    function.
+_LIBCPP_FUNC_VIS
+bool __libcpp_set_debug_function(__libcpp_debug_function_type __func);
+
+// Setup the throwing debug handler during dynamic initialization.
+#if _LIBCPP_DEBUG_LEVEL >= 1 && defined(_LIBCPP_DEBUG_USE_EXCEPTIONS)
+static bool __init_dummy = __libcpp_set_debug_function(__libcpp_throw_debug_function);
+#endif
+
+#if _LIBCPP_DEBUG_LEVEL >= 1 || defined(_LIBCPP_BUILDING_LIBRARY)
+class _LIBCPP_EXCEPTION_ABI __libcpp_debug_exception : public exception {
+public:
+  __libcpp_debug_exception() _NOEXCEPT;
+  explicit __libcpp_debug_exception(__libcpp_debug_info const& __i);
+  __libcpp_debug_exception(__libcpp_debug_exception const&);
+  ~__libcpp_debug_exception() _NOEXCEPT;
+  const char* what() const _NOEXCEPT;
+private:
+  struct __libcpp_debug_exception_imp;
+  __libcpp_debug_exception_imp *__imp_;
+};
+#endif
+
+#if _LIBCPP_DEBUG_LEVEL >= 2 || defined(_LIBCPP_BUILDING_LIBRARY)
+
 struct _LIBCPP_TYPE_VIS __c_node;
 
 struct _LIBCPP_TYPE_VIS __i_node
@@ -115,7 +169,7 @@
 };
 
 template <class _Cont>
-bool
+inline bool
 _C_node<_Cont>::__dereferenceable(const void* __i) const
 {
     typedef typename _Cont::const_iterator iterator;
@@ -125,7 +179,7 @@
 }
 
 template <class _Cont>
-bool
+inline bool
 _C_node<_Cont>::__decrementable(const void* __i) const
 {
     typedef typename _Cont::const_iterator iterator;
@@ -135,7 +189,7 @@
 }
 
 template <class _Cont>
-bool
+inline bool
 _C_node<_Cont>::__addable(const void* __i, ptrdiff_t __n) const
 {
     typedef typename _Cont::const_iterator iterator;
@@ -145,7 +199,7 @@
 }
 
 template <class _Cont>
-bool
+inline bool
 _C_node<_Cont>::__subscriptable(const void* __i, ptrdiff_t __n) const
 {
     typedef typename _Cont::const_iterator iterator;
@@ -227,9 +281,9 @@
 _LIBCPP_FUNC_VIS const __libcpp_db* __get_const_db();
 
 
-_LIBCPP_END_NAMESPACE_STD
+#endif // _LIBCPP_DEBUG_LEVEL >= 2 || defined(_LIBCPP_BUILDING_LIBRARY)
 
-#endif
+_LIBCPP_END_NAMESPACE_STD
 
 #endif  // _LIBCPP_DEBUG_H
 
diff --git a/lib/abi/CHANGELOG.TXT b/lib/abi/CHANGELOG.TXT
index 488d7b7..bccca2e 100644
--- a/lib/abi/CHANGELOG.TXT
+++ b/lib/abi/CHANGELOG.TXT
@@ -16,6 +16,28 @@
 Version 4.0
 -----------
 
+* rTBD - Add _LIBCPP_ASSERT debug handling functions
+
+  All Platforms
+  -------------
+  Symbol added: _ZNSt3__124__libcpp_debug_exceptionC2ERKNS_19__libcpp_debug_infoE
+  Symbol added: _ZNSt3__124__libcpp_debug_exceptionD1Ev
+  Symbol added: _ZTINSt3__124__libcpp_debug_exceptionE
+  Symbol added: _ZNSt3__129__libcpp_throw_debug_functionERKNS_19__libcpp_debug_infoE
+  Symbol added: _ZNSt3__124__libcpp_debug_exceptionD2Ev
+  Symbol added: _ZNSt3__129__libcpp_abort_debug_functionERKNS_19__libcpp_debug_infoE
+  Symbol added: _ZNSt3__124__libcpp_debug_exceptionC2ERKS0_
+  Symbol added: _ZNSt3__124__libcpp_debug_exceptionC1Ev
+  Symbol added: _ZNSt3__124__libcpp_debug_exceptionC1ERKNS_19__libcpp_debug_infoE
+  Symbol added: _ZNSt3__124__libcpp_debug_exceptionC2Ev
+  Symbol added: _ZTSNSt3__124__libcpp_debug_exceptionE
+  Symbol added: _ZNSt3__123__libcpp_debug_functionE
+  Symbol added: _ZNKSt3__124__libcpp_debug_exception4whatEv
+  Symbol added: _ZNSt3__124__libcpp_debug_exceptionC1ERKS0_
+  Symbol added: _ZNSt3__124__libcpp_debug_exceptionD0Ev
+  Symbol added: _ZTVNSt3__124__libcpp_debug_exceptionE
+  Symbol added: _ZNSt3__127__libcpp_set_debug_functionEPFvRKNS_19__libcpp_debug_infoEE
+
 * r288547 - Implement C++17 <variant>
 
   All Platforms
diff --git a/lib/abi/x86_64-apple-darwin16.0.0.abilist b/lib/abi/x86_64-apple-darwin16.0.0.abilist
index 1b6acad..f7218a4 100644
--- a/lib/abi/x86_64-apple-darwin16.0.0.abilist
+++ b/lib/abi/x86_64-apple-darwin16.0.0.abilist
@@ -262,6 +262,7 @@
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNKSt3__121__basic_string_commonILb1EE20__throw_out_of_rangeEv'}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNKSt3__123__match_any_but_newlineIcE6__execERNS_7__stateIcEE'}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNKSt3__123__match_any_but_newlineIwE6__execERNS_7__stateIwEE'}
+{'type': 'FUNC', 'is_defined': True, 'name': '__ZNKSt3__124__libcpp_debug_exception4whatEv'}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNKSt3__15ctypeIcE10do_tolowerEPcPKc'}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNKSt3__15ctypeIcE10do_tolowerEc'}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNKSt3__15ctypeIcE10do_toupperEPcPKc'}
@@ -1212,6 +1213,16 @@
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__121recursive_timed_mutexD1Ev'}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__121recursive_timed_mutexD2Ev'}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__121undeclare_no_pointersEPcm'}
+{'type': 'OBJECT', 'is_defined': True, 'name': '__ZNSt3__123__libcpp_debug_functionE', 'size': 0}
+{'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__124__libcpp_debug_exceptionC1ERKNS_19__libcpp_debug_infoE'}
+{'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__124__libcpp_debug_exceptionC1ERKS0_'}
+{'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__124__libcpp_debug_exceptionC1Ev'}
+{'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__124__libcpp_debug_exceptionC2ERKNS_19__libcpp_debug_infoE'}
+{'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__124__libcpp_debug_exceptionC2ERKS0_'}
+{'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__124__libcpp_debug_exceptionC2Ev'}
+{'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__124__libcpp_debug_exceptionD0Ev'}
+{'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__124__libcpp_debug_exceptionD1Ev'}
+{'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__124__libcpp_debug_exceptionD2Ev'}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__125notify_all_at_thread_exitERNS_18condition_variableENS_11unique_lockINS_5mutexEEE'}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__127__insertion_sort_incompleteIRNS_6__lessIaaEEPaEEbT0_S5_T_'}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__127__insertion_sort_incompleteIRNS_6__lessIccEEPcEEbT0_S5_T_'}
@@ -1228,6 +1239,9 @@
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__127__insertion_sort_incompleteIRNS_6__lessIwwEEPwEEbT0_S5_T_'}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__127__insertion_sort_incompleteIRNS_6__lessIxxEEPxEEbT0_S5_T_'}
 {'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__127__insertion_sort_incompleteIRNS_6__lessIyyEEPyEEbT0_S5_T_'}
+{'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__127__libcpp_set_debug_functionEPFvRKNS_19__libcpp_debug_infoEE'}
+{'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__129__libcpp_abort_debug_functionERKNS_19__libcpp_debug_infoE'}
+{'type': 'FUNC', 'is_defined': True, 'name': '__ZNSt3__129__libcpp_throw_debug_functionERKNS_19__libcpp_debug_infoE'}
 {'type': 'OBJECT', 'is_defined': True, 'name': '__ZNSt3__13cinE', 'size': 0}
 {'type': 'OBJECT', 'is_defined': True, 'name': '__ZNSt3__14cerrE', 'size': 0}
 {'type': 'OBJECT', 'is_defined': True, 'name': '__ZNSt3__14clogE', 'size': 0}
@@ -1651,6 +1665,7 @@
 {'type': 'OBJECT', 'is_defined': True, 'name': '__ZTINSt3__120__codecvt_utf8_utf16IwEE', 'size': 0}
 {'type': 'OBJECT', 'is_defined': True, 'name': '__ZTINSt3__120__time_get_c_storageIcEE', 'size': 0}
 {'type': 'OBJECT', 'is_defined': True, 'name': '__ZTINSt3__120__time_get_c_storageIwEE', 'size': 0}
+{'type': 'OBJECT', 'is_defined': True, 'name': '__ZTINSt3__124__libcpp_debug_exceptionE', 'size': 0}
 {'type': 'OBJECT', 'is_defined': True, 'name': '__ZTINSt3__15ctypeIcEE', 'size': 0}
 {'type': 'OBJECT', 'is_defined': True, 'name': '__ZTINSt3__15ctypeIwEE', 'size': 0}
 {'type': 'OBJECT', 'is_defined': True, 'name': '__ZTINSt3__16locale5facetE', 'size': 0}
@@ -2182,6 +2197,7 @@
 {'type': 'OBJECT', 'is_defined': True, 'name': '__ZTVNSt3__120__codecvt_utf8_utf16IDiEE', 'size': 0}
 {'type': 'OBJECT', 'is_defined': True, 'name': '__ZTVNSt3__120__codecvt_utf8_utf16IDsEE', 'size': 0}
 {'type': 'OBJECT', 'is_defined': True, 'name': '__ZTVNSt3__120__codecvt_utf8_utf16IwEE', 'size': 0}
+{'type': 'OBJECT', 'is_defined': True, 'name': '__ZTVNSt3__124__libcpp_debug_exceptionE', 'size': 0}
 {'type': 'OBJECT', 'is_defined': True, 'name': '__ZTVNSt3__15ctypeIcEE', 'size': 0}
 {'type': 'OBJECT', 'is_defined': True, 'name': '__ZTVNSt3__15ctypeIwEE', 'size': 0}
 {'type': 'OBJECT', 'is_defined': True, 'name': '__ZTVNSt3__16locale5facetE', 'size': 0}
diff --git a/lib/abi/x86_64-unknown-linux-gnu.abilist b/lib/abi/x86_64-unknown-linux-gnu.abilist
index a802ae4..7282fa7 100644
--- a/lib/abi/x86_64-unknown-linux-gnu.abilist
+++ b/lib/abi/x86_64-unknown-linux-gnu.abilist
@@ -252,6 +252,7 @@
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNKSt3__121__basic_string_commonILb1EE20__throw_out_of_rangeEv'}
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNKSt3__123__match_any_but_newlineIcE6__execERNS_7__stateIcEE'}
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNKSt3__123__match_any_but_newlineIwE6__execERNS_7__stateIwEE'}
+{'is_defined': True, 'type': 'FUNC', 'name': '_ZNKSt3__124__libcpp_debug_exception4whatEv'}
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNKSt3__15ctypeIcE10do_tolowerEPcPKc'}
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNKSt3__15ctypeIcE10do_tolowerEc'}
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNKSt3__15ctypeIcE10do_toupperEPcPKc'}
@@ -1136,6 +1137,16 @@
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__121recursive_timed_mutexD1Ev'}
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__121recursive_timed_mutexD2Ev'}
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__121undeclare_no_pointersEPcm'}
+{'is_defined': True, 'type': 'OBJECT', 'name': '_ZNSt3__123__libcpp_debug_functionE', 'size': 8}
+{'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__124__libcpp_debug_exceptionC1ERKNS_19__libcpp_debug_infoE'}
+{'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__124__libcpp_debug_exceptionC1ERKS0_'}
+{'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__124__libcpp_debug_exceptionC1Ev'}
+{'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__124__libcpp_debug_exceptionC2ERKNS_19__libcpp_debug_infoE'}
+{'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__124__libcpp_debug_exceptionC2ERKS0_'}
+{'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__124__libcpp_debug_exceptionC2Ev'}
+{'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__124__libcpp_debug_exceptionD0Ev'}
+{'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__124__libcpp_debug_exceptionD1Ev'}
+{'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__124__libcpp_debug_exceptionD2Ev'}
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__125__num_get_signed_integralIlEET_PKcS3_Rji'}
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__125__num_get_signed_integralIxEET_PKcS3_Rji'}
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__125notify_all_at_thread_exitERNS_18condition_variableENS_11unique_lockINS_5mutexEEE'}
@@ -1154,10 +1165,13 @@
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__127__insertion_sort_incompleteIRNS_6__lessIwwEEPwEEbT0_S5_T_'}
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__127__insertion_sort_incompleteIRNS_6__lessIxxEEPxEEbT0_S5_T_'}
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__127__insertion_sort_incompleteIRNS_6__lessIyyEEPyEEbT0_S5_T_'}
+{'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__127__libcpp_set_debug_functionEPFvRKNS_19__libcpp_debug_infoEE'}
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__127__num_get_unsigned_integralIjEET_PKcS3_Rji'}
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__127__num_get_unsigned_integralImEET_PKcS3_Rji'}
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__127__num_get_unsigned_integralItEET_PKcS3_Rji'}
 {'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__127__num_get_unsigned_integralIyEET_PKcS3_Rji'}
+{'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__129__libcpp_abort_debug_functionERKNS_19__libcpp_debug_infoE'}
+{'is_defined': True, 'type': 'FUNC', 'name': '_ZNSt3__129__libcpp_throw_debug_functionERKNS_19__libcpp_debug_infoE'}
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZNSt3__13cinE', 'size': 168}
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZNSt3__14cerrE', 'size': 160}
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZNSt3__14clogE', 'size': 160}
@@ -1554,6 +1568,7 @@
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZTINSt3__120__codecvt_utf8_utf16IwEE', 'size': 24}
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZTINSt3__120__time_get_c_storageIcEE', 'size': 16}
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZTINSt3__120__time_get_c_storageIwEE', 'size': 16}
+{'is_defined': True, 'type': 'OBJECT', 'name': '_ZTINSt3__124__libcpp_debug_exceptionE', 'size': 24}
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZTINSt3__15ctypeIcEE', 'size': 56}
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZTINSt3__15ctypeIwEE', 'size': 56}
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZTINSt3__16locale5facetE', 'size': 24}
@@ -1679,6 +1694,7 @@
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZTSNSt3__120__codecvt_utf8_utf16IwEE', 'size': 34}
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZTSNSt3__120__time_get_c_storageIcEE', 'size': 34}
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZTSNSt3__120__time_get_c_storageIwEE', 'size': 34}
+{'is_defined': True, 'type': 'OBJECT', 'name': '_ZTSNSt3__124__libcpp_debug_exceptionE', 'size': 35}
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZTSNSt3__15ctypeIcEE', 'size': 18}
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZTSNSt3__15ctypeIwEE', 'size': 18}
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZTSNSt3__16locale5facetE', 'size': 22}
@@ -1790,6 +1806,7 @@
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZTVNSt3__120__codecvt_utf8_utf16IDiEE', 'size': 96}
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZTVNSt3__120__codecvt_utf8_utf16IDsEE', 'size': 96}
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZTVNSt3__120__codecvt_utf8_utf16IwEE', 'size': 96}
+{'is_defined': True, 'type': 'OBJECT', 'name': '_ZTVNSt3__124__libcpp_debug_exceptionE', 'size': 40}
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZTVNSt3__15ctypeIcEE', 'size': 104}
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZTVNSt3__15ctypeIwEE', 'size': 136}
 {'is_defined': True, 'type': 'OBJECT', 'name': '_ZTVNSt3__16locale5facetE', 'size': 40}
diff --git a/src/debug.cpp b/src/debug.cpp
index d46935c..fe27dc8 100644
--- a/src/debug.cpp
+++ b/src/debug.cpp
@@ -7,16 +7,75 @@
 //
 //===----------------------------------------------------------------------===//
 
-#define _LIBCPP_DEBUG 1
 #include "__config"
 #include "__debug"
 #include "functional"
 #include "algorithm"
+#include "string"
+#include "cstdio"
 #include "__hash_table"
 #include "mutex"
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
+static std::string make_what_str(__libcpp_debug_info const& info) {
+  string msg = info.__file_;
+  msg += ":" + to_string(info.__line_) + ": _LIBCPP_ASSERT '";
+  msg += info.__pred_;
+  msg += "' failed. ";
+  msg += info.__msg_;
+  return msg;
+}
+
+_LIBCPP_SAFE_STATIC __libcpp_debug_function_type
+    __libcpp_debug_function = __libcpp_abort_debug_function;
+
+bool __libcpp_set_debug_function(__libcpp_debug_function_type __func) {
+  __libcpp_debug_function = __func;
+  return true;
+}
+
+_LIBCPP_NORETURN void __libcpp_abort_debug_function(__libcpp_debug_info const& info) {
+  std::fprintf(stderr, "%s\n", make_what_str(info).c_str());
+  std::abort();
+}
+
+_LIBCPP_NORETURN void __libcpp_throw_debug_function(__libcpp_debug_info const& info) {
+  throw __libcpp_debug_exception(info);
+}
+
+struct __libcpp_debug_exception::__libcpp_debug_exception_imp {
+  __libcpp_debug_info __info_;
+  std::string __what_str_;
+};
+
+__libcpp_debug_exception::__libcpp_debug_exception() _NOEXCEPT
+    : __imp_(nullptr) {
+}
+
+__libcpp_debug_exception::__libcpp_debug_exception(
+    __libcpp_debug_info const& info) : __imp_(new __libcpp_debug_exception_imp)
+{
+  __imp_->__info_ = info;
+  __imp_->__what_str_ = make_what_str(info);
+}
+__libcpp_debug_exception::__libcpp_debug_exception(
+    __libcpp_debug_exception const& other) : __imp_(nullptr) {
+  if (other.__imp_)
+    __imp_ = new __libcpp_debug_exception_imp(*other.__imp_);
+}
+
+__libcpp_debug_exception::~__libcpp_debug_exception() _NOEXCEPT {
+  if (__imp_)
+    delete __imp_;
+}
+
+const char* __libcpp_debug_exception::what() const _NOEXCEPT {
+  if (__imp_)
+    return __imp_->__what_str_.c_str();
+  return "__libcpp_debug_exception";
+}
+
 _LIBCPP_FUNC_VIS
 __libcpp_db*
 __get_db()
diff --git a/test/libcxx/debug/debug_abort.pass.cpp b/test/libcxx/debug/debug_abort.pass.cpp
new file mode 100644
index 0000000..cfe6320
--- /dev/null
+++ b/test/libcxx/debug/debug_abort.pass.cpp
@@ -0,0 +1,30 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// Test that the default debug handler aborts the program.
+
+#define _LIBCPP_DEBUG 0
+
+#include <csignal>
+#include <cstdlib>
+#include <__debug>
+
+void signal_handler(int signal)
+{
+    if (signal == SIGABRT)
+      std::_Exit(EXIT_SUCCESS);
+    std::_Exit(EXIT_FAILURE);
+}
+
+int main()
+{
+  if (std::signal(SIGABRT, signal_handler) != SIG_ERR)
+    _LIBCPP_ASSERT(false, "foo");
+  return EXIT_FAILURE;
+}
diff --git a/test/libcxx/debug/debug_throw.pass.cpp b/test/libcxx/debug/debug_throw.pass.cpp
new file mode 100644
index 0000000..109f9e9
--- /dev/null
+++ b/test/libcxx/debug/debug_throw.pass.cpp
@@ -0,0 +1,36 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// UNSUPPORTED: libcpp-no-exceptions
+
+// Test that the default debug handler can be overridden and test the
+// throwing debug handler.
+
+#define _LIBCPP_DEBUG 0
+
+#include <cstdlib>
+#include <exception>
+#include <type_traits>
+#include <__debug>
+
+int main()
+{
+  {
+    std::__libcpp_debug_function = std::__libcpp_throw_debug_function;
+    try {
+      _LIBCPP_ASSERT(false, "foo");
+    } catch (std::__libcpp_debug_exception const&) {}
+  }
+  {
+    // test that the libc++ exception type derives from std::exception
+    static_assert(std::is_base_of<std::exception,
+                                  std::__libcpp_debug_exception
+                  >::value, "must be an exception");
+  }
+}
diff --git a/test/libcxx/debug/debug_throw_register.pass.cpp b/test/libcxx/debug/debug_throw_register.pass.cpp
new file mode 100644
index 0000000..21b1d52
--- /dev/null
+++ b/test/libcxx/debug/debug_throw_register.pass.cpp
@@ -0,0 +1,30 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// UNSUPPORTED: libcpp-no-exceptions
+
+// Test that defining _LIBCPP_DEBUG_USE_EXCEPTIONS causes _LIBCPP_ASSERT
+// to throw on failure.
+
+#define _LIBCPP_DEBUG 1
+#define _LIBCPP_DEBUG_USE_EXCEPTIONS
+
+#include <cstdlib>
+#include <exception>
+#include <type_traits>
+#include <__debug>
+#include <cassert>
+
+int main()
+{
+  try {
+    _LIBCPP_ASSERT(false, "foo");
+    assert(false);
+  } catch (...) {}
+}
diff --git a/www/debug_mode.html b/www/debug_mode.html
deleted file mode 100644
index 943c47d..0000000
--- a/www/debug_mode.html
+++ /dev/null
@@ -1,162 +0,0 @@
-<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
-        "http://www.w3.org/TR/html4/strict.dtd">
-<html>
-<head>
-	<title>libc++ debug mode status</title>
-</head>
-<body>
-
-<p>
-Work is beginning on a libc++ debug mode.  The purpose of this table is to
-record which parts of libc++ have debug mode support.
-</p>
-
-<p>
-Note: Debug mode is currently not functional. Defining _LIBCPP_DEBUG will result
-in fairly nasty compile errors.
-</p>
-
-<table border=1>
-<tr>
-<th>Section</th>
-<th>Completed ?</th>
-</tr>
-
-<tr>
-<td>
-<p>
-<code>vector&lt;T&gt;, T != bool</code>
-</p>
-</td>
-<td align="center"> &#10003; </td>
-</tr>
-
-<tr>
-<td>
-<p>
-<code>&lt;list&gt;</code>
-</p>
-</td>
-<td align="center"> &#10003; </td>
-</tr>
-
-<tr>
-<td>
-<p>
-<code>&lt;unordered_set&gt;</code>
-</p>
-</td>
-<td align="center"> &#10003; </td>
-</tr>
-
-<tr>
-<td>
-<p>
-<code>&lt;unordered_map&gt;</code>
-</p>
-</td>
-<td align="center"> &#10003; </td>
-</tr>
-
-<tr>
-<td>
-<p>
-<code>&lt;string&gt;</code>
-</p>
-</td>
-<td align="center"> &#10003; </td>
-</tr>
-
-<tr>
-<td>
-<p>
-<code>&lt;set&gt;</code>
-</p>
-</td>
-<td align="center"><!-- &#10003; --></td>
-</tr>
-
-<tr>
-<td>
-<p>
-<code>&lt;map&gt;</code>
-</p>
-</td>
-<td align="center"><!-- &#10003; --></td>
-</tr>
-
-<tr>
-<td>
-<p>
-<code>vector&lt;bool&gt;</code>
-</p>
-</td>
-<td align="center"><!-- &#10003; --></td>
-</tr>
-
-<tr>
-<td>
-<p>
-<code>&lt;deque&gt;</code>
-</p>
-</td>
-<td align="center"><!-- &#10003; --></td>
-</tr>
-
-<tr>
-<td>
-<p>
-<code>&lt;forward_list&gt;</code>
-</p>
-</td>
-<td align="center"><!-- &#10003; --></td>
-</tr>
-
-<tr>
-<td>
-<p>
-<code>&lt;array&gt;</code>
-</p>
-</td>
-<td align="center"><!-- &#10003; --></td>
-</tr>
-
-<tr>
-<td>
-<p>
-<code>&lt;stack&gt;</code>
-</p>
-</td>
-<td align="center"><!-- &#10003; --></td>
-</tr>
-
-<tr>
-<td>
-<p>
-<code>&lt;queue&gt;</code>
-</p>
-</td>
-<td align="center"><!-- &#10003; --></td>
-</tr>
-
-<tr>
-<td>
-<p>
-<code>&lt;algorithm&gt;</code>
-</p>
-</td>
-<td align="center"><!-- &#10003; --></td>
-</tr>
-
-
-</table>
-
-<p>
-At present the table is known to not be a complete list.  It is currently ordered
-in approximate priority order.
-</p>
-
-<p>Last Updated: 3-June-2014</p>
-
-</body>
-</html>
diff --git a/www/index.html b/www/index.html
index e0f02f2..6b464eb 100644
--- a/www/index.html
+++ b/www/index.html
@@ -220,7 +220,6 @@
 <li><a href="atomic_design.html"><tt>&lt;atomic&gt;</tt></a></li>
 <li><a href="type_traits_design.html"><tt>&lt;type_traits&gt;</tt></a></li>
 <li><a href="http://cplusplusmusings.wordpress.com/2012/07/05/clang-and-standard-libraries-on-mac-os-x/">Excellent notes by Marshall Clow</a></li>
-<li><a href="debug_mode.html">Status of debug mode</a></li>
 </ul>
 
 </div>