I have some programs in F77 which I compile on ABSoft Windows without problem. I want to compile it on MacOs X 10.7 with gfortran, I use for example :   gfortran -c module1.f gfortran -c module2.f gfortran -c principal.f gfortran -o Appli.exe principal.o module1.o module1.o Then I have an error message after the last line : Undefined symbols for architecture x8664: "main", symbol(s) not found for architecture x86_64 collect2: error: ld returned 1 exit status May you help me Many thanks