  I discuss the role of quantum effects in the phenomenology of effective
supergravity theories from compactification of the weakly coupled heterotic
string. An accurate incorporation of these effects requires a regularization
procedure that respects local supersymmetry and BRST invariance and that
retains information associated with the cut-off scale, which has physical
meaning in an effective theory. I briefly outline the Pauli-Villars
regularization procedure, describe some applications, and comment on what
remains to be done to fully define the effective quantum field theory.
