OK, I have a header file (structs.h) that includes windows.h and glgl.h to use certain typedefs in a structure or two. Now, if I am not mistaken, since ogl.cpp includes structs.h, shouldn't it already have included windows.h and gl.h? You see, if I don't include the two headers in the cpp file as well, it spews multiple declaration errors or other such garbage. I didn't want to have to include gl.h in my MAIN module, but since it also includes structs.h, it seems as though I MUST includ gl.h or get errors. Why is this?