As mentioned previously, &SCons; will build every target in or below the current directory by default--that is, when you don't explicitly specify one or more targets on the command line. Sometimes, however, you may want to specify explicitly that only certain programs should be built by default. You do this with the &Default; function: env = Environment() hello = env.Program('hello.c') env.Program('goodbye.c') Default(hello) hello.c goodbye.c This &SConstruct; file knows how to build two programs, &hello; and &goodbye;, but only builds the &hello; program by default: scons scons scons goodbye Note that, even when you use the &Default; function in your &SConstruct; file, you can still explicitly specify the current directory (.) on the command line to tell &SCons; to build everything in (or below) the current directory: scons . You can also call the &Default; function more than once, in which case each call adds to the list of targets to be built by default: env = Environment() prog1 = env.Program('prog1.c') Default(prog1) prog2 = env.Program('prog2.c') prog3 = env.Program('prog3.c') Default(prog3) prog1.c prog2.c prog3.c Or you can specify more than one target in a single call to the &Default; function: env = Environment() prog1 = env.Program('prog1.c') prog2 = env.Program('prog2.c') prog3 = env.Program('prog3.c') Default(prog1, prog3) Either of these last two examples will build only the prog1 and prog3 programs by default: scons scons . Lastly, if for some reason you don't want any targets built by default, you can use the Python None variable: env = Environment() prog1 = env.Program('prog1.c') prog2 = env.Program('prog2.c') Default(None) prog1.c prog2.c Which would produce build output like: scons scons .