  Results on soft and hard diffraction are briefly reviewed and placed in a QCD
perspective using a parton model approach. Issues addressed include
factorization, scaling properties, universality of rapidity gap formation, and
unitarity. Predictions for differential cross sections of processes with
multiple rapidity gaps are presented with examples for the Tevatron and the
Large Hadron Collider. This paper is an expanded version of a paper delivered
at SNOWMASS-2001 (arXiv:hep-ph/0110240).
