Hi, I have built the regex library as per instructions, using a command prompt set up by Visual Studio. When I come to build my project using the library, it automaticaly pulls in the regex lib file, but I get multiple defined symbols from the linker: Linking... libboost_regex-vc80-mt-gd-1_33_1.lib(usinstances.obj) : error LNK2005: "public: static unsigned int __cdecl std::char_traits<unsigned short>::length(unsigned short const *)" (?length@?$char_traits@G@std@@SAIPBG@Z) already defined in msvcprtd.lib(MSVCP80D.dll) libboost_regex-vc80-mt-gd-1_33_1.lib(usinstances.obj) : error LNK2005: "public: __thiscall std::allocator<unsigned short>::allocator<unsigned short>(void)" (??0?$allocator@G@std@@QAE@XZ) already defined in msvcprtd.lib(MSVCP80D.dll) My app is built with wchar_t as unsigned short, and with UNICODE and _UNICODE defined, so I updated the makefile for this and rebuilt, but I just get the same thing. I can't even see how usinstances.cpp or any other file defines these things, and searching boost and the web reveals nothing. Any ideas, anyone? Thanks, Simon