Yuck. We had something similar in my last job. How we got stuff to work: 1. All the FORTRAN stuff was self-contained in its own static library. 2. Any functions interfacing to C++ were clearly designated in a header/source file that wrapped around the Fortran. 3. Be really careful with strings, as they are encoded differently in Fortran and C++. It was still a pain in the butt, but that's how we did it. The suggestion somebody else mentioned to use a DLL would also work pretty well, we did that in some other cases. Even a broken clock is right twice a day.