We describe in this paper the compilation scheme of the GNU Prolog system. This system is built on our previous experience of compiling Prolog to C in wamcc. The compilation scheme has been however redesigned to overcome drawbacks of the compilation to C. In particular, GNU-Prolog is based on a low-level mini-assembly platformindependent language that makes it possible to avoid the phase of compiling C code, and thus speeds up drastically compilation time. It also makes it possible to produce small stand alone executable files as the result of the compilation process. Interestingly, GNU Prolog is now compliant to the ISO standard and includes several extensions (constraint solving, OS interface, sockets, global variables, etc). The overall system is efficient and comparable in performances with commercial systems.