John M. MacDonald is professor of criminology and sociology at the University of Pennsylvania. His current research focus is on how policies and programs to change the land use of places can reduce crime and violence in neighborhoods. This research includes a randomized community trial of the effect of vacant lot remediation and stabilization on violence and injury outcomes, and a randomized trial of abandoned housing remediation on substance abuse and violence. He also studies racial disparities in criminal justice processing and ways to reduce these disparities through policy and program reforms.