diff --git a/Installation/include/CGAL/config.h b/Installation/include/CGAL/config.h
index b4e1f998644..8296a753ad9 100644
--- a/Installation/include/CGAL/config.h
+++ b/Installation/include/CGAL/config.h
@@ -232,14 +232,24 @@ make_list(Iterator begin, Iterator end)
 #  define CGAL_make_list(begin, end) (begin, end)
 #endif
 
-#if (__GNUC__ > 3 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 1))
-#define CGAL_DEPRECATED  __attribute__((deprecated))
-#elif _MSC_VER > 1300
-#define CGAL_DEPRECATED __declspec(deprecated)
+
+// Macro to trigger deprecation warnings
+#if defined (__GNUC__) && (__GNUC__ > 3 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 1))
+#  define CGAL_DEPRECATED __attribute__((deprecated))
+#elif defined (_MSC_VER) && (_MSC_VER > 1300)
+#  define CGAL_DEPRECATED __declspec(deprecated)
 #else
-#define CGAL_DEPRECATED
+#  define CGAL_DEPRECATED
 #endif
 
 
+// If CGAL_HAS_THREADS is not defined, then CGAL code assumes
+// it can do any thread-unsafe things (like using static variables).
+#if !defined CGAL_HAS_THREADS && !defined CGAL_HAS_NO_THREADS
+  #if defined BOOST_HAS_THREADS || defined _OPENMP
+  #  define CGAL_HAS_THREADS
+  #endif
+#endif
+
 
 #endif // CGAL_CONFIG_H
diff --git a/Manual/doc_tex/Introduction/main.tex b/Manual/doc_tex/Introduction/main.tex
index eac11cf8a87..b1444a2442e 100644
--- a/Manual/doc_tex/Introduction/main.tex
+++ b/Manual/doc_tex/Introduction/main.tex
@@ -154,5 +154,22 @@ Every release of \cgal\ defines the following preprocessor macros:
 \end{description}
  
 
+\section{Thread safety}
+
+\cgal\ is progressively being made thread-safe.  The guidelines which are followed
+are:
+\begin{itemize}
+\item it should be possible to use different objects in different threads at
+the same time (of the same type or not),
+\item it is not safe to access the same object from different threads
+at the same time.
+\end{itemize}
+
+If the macro \ccc{CGAL_HAS_THREADS} is not defined, then \cgal\ assumes it can use
+any thread-unsafe code (such as static variables).  By default, this macro is not
+defined, unless \ccc{BOOST_HAS_THREADS} or \ccc{_OPENMP} is defined.  It is possible
+to force its definition on the command line, and it is possible to prevent its default
+definition by setting \ccc{CGAL_HAS_NO_THREADS} from the command line.
+
 
 \input{Introduction_ref/checks} % extra chapter