Attempting to compile and link the following code with a default build of 1.36 on OS X 10.5.4 (Intel) // test.cpp #include <fstream> #include <iostream> #include <string> #include <vector> //#include <boost/system/error_code.hpp> //#include <boost/system/system_error.hpp> #include <boost/filesystem/operations.hpp> #include <boost/filesystem/path.hpp> int main (int argc, char * const argv[]) { boost::filesystem::create_directory("blah"); return 0; } results in a linker error, even though the method in question is defined inline in <boost/system/error_code.hpp> : Undefined symbols: "boost::system::error_code::message() const", referenced from: boost::system::system_error::what() constin ccyMBSNr.o ld: symbol(s) not found collect2: ld returned 1 exit status This is reproducible both from a clean XCode 3.0 project and from the command line : gcc test.cpp -I/usr/local/include -I .. -L/usr/local/lib - lboost_filesystem-xgcc40-mt -lboost_system-xgcc40-mt -lstdc++ Uncommenting the explicit includes doesn't help, either. This is a weird one... Matthias