John Pfaff is a law professor at Fordham University where he teaches criminal law, sentencing law, and law and economics. Before joining Fordham, he was the John M. Olin fellow at the Northwestern University School of Law and clerked for Judge Stephen F. Williams on the U.S. Court of Appeals for the D.C. Circuit.

Professor Pfaff's research focuses primarily on empirical matters related to criminal justice, especially criminal sentencing. He has paid particular attention to identifying the causes of the unprecedented 40-year boom in U.S. incarceration rates. His recent work illuminates the previously under-appreciated role of prosecutorial discretion in driving up prison populations.