Hallo, After building Boost 1.31 with the borland toolset I noticed that some symbols were missing from the Boost.Signals DLL's. More specifically all the symbols exported from libs/signals/src/signal_base.cpp are not exported. This appears to be caused by the explicit inclusion of boost/signals/detail/config.hpp in boost/signals/detail/signal_base.hpp. The effect of this inclusion is to miss the indirect inclusion of boost/config.hpp . After removing the #include <boost/signals/detail/config.hpp> line from signal_base.hpp the DLL's build correctly. Note that while I only tested with the borland toolset this problem is potentially present on all the win32 toolsets. Cheers, Nicola Musatti