Diffraction in QCD

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).