By default, &SCons; removes targets before building them. Sometimes, however, this is not what you want. For example, you may want to update a library incrementally, not by having it deleted and then rebuilt from all of the constituent object files. In such cases, you can use the &Precious; method to prevent &SCons; from removing the target before it is built: env = Environment(XXX NEED LIBRARY FLAGS LIBFLAGS = '-r') lib = env.Library('foo', ['f1.c', 'f2.c', 'f3.c']) env.Precious(lib) int f1() { } int f2() { } int f3() { } XXX: scons &SCons; will still delete files marked as &Precious; when the -c option is used.