Hello, I have a very special problem concerning boost::noncopyable under Windows in a shared library. A class deriving from boost::noncopyable becomes copyable. Strange ? Here is the example code. (Using Visual Studio 2005, no sp, Windows XP): 1) create one static lib with only TestClasses.hpp with the following content in it: #include <boost/noncopyable.hpp> class INonCopyNormalClass: boost::noncopyable { public: virtual INonCopyNormalClass* clone() = 0; }; 2) create one DLL (shared lib) with the following content: DLLMain.hpp: #include "../TestLib/TestClasses.hpp" # if defined(UNCOPYABLETESTDLL_EXPORTS) # define DLL_API __declspec(dllexport) # else # define DLL_API # endif class DLL_API AnotherNonNormalCopyClass: public INonCopyNormalClass { }; class YetAnotherNonNormalCopyClass: public AnotherNonNormalCopyClass { public: YetAnotherNonNormalCopyClass(); virtual INonCopyNormalClass* clone(); }; DLLMain.cpp: #include "DLLmain.hpp" YetAnotherNonNormalCopyClass::YetAnotherNonNormalCopyClass() { } INonCopyNormalClass* YetAnotherNonNormalCopyClass::clone() { return new YetAnotherNonNormalCopyClass(*this); } It is quite important that the DLL_API is defined properly !! This seems to be the reason, that the code above compile, links and runs. This should not be possible. The line return new YetAnotherNonNormalCopyClass(*this); should not work. If DLL_API is undefined or removed, you will get the correct error message and compilation fails ANY ideas ? SOMEONE ? Thanks and best, Philipp