After a quick look at the documentation and user list messages I have found that using Boost.Python with msvc MTd or MT Runtime Libraries may have some problems. My first try with Boost.Python gave me this error: c:\work\src\boost_1_43_0\boost/config/auto_link.hpp(297) : fatal error C1189: #error : "Mixing a dll boost library with a static runtime is a really bad idea..." Then I found that it was possible to use the BOOST_PYTHON_STATIC_LIB macro. This worked fine. I am using python 3.1, I have installed both the x86 and x64 python versions in different directories. Can someone explain me why I need to specify this macro and why "Mixing a dll boost library with a static runtime is a really bad idea"? Regards, Isaac Lascasas.