How to compile: First, install Geant4. Make sure all your G4* environment variables are set. Then simply ./configure [answer the question] make The executable binary will be in $G4WORK/$G4SYSTEM/glg4sim. If you are _re_compiling after moving directories around, then do a "make clean" before the "make", to delete any dependency files left around from compilation in the other directories. Sometimes "make clean" is necessary under other circumstances, too. A general rule for big C++ projects is: if "make" fails after a change, try "make clean && make".