There is a growing U.S. national consensus that with proper attention to the policies that drive the size of prison populations, these populations can be reduced. As several states have reduced prison populations, there is an accumulating record of strategies that reduce prison populations—but little in the way of proven cause and effect based on research or evidence of the degree to which these gains can be sustained and replicated. Concurrently, the current fiscal crisis has created enormous pressure to reduce prison populations, with a first-in-decades showing of political support. This article provides information about the various prison-reduction strategies, with examples of successful initiatives and an eye toward implementing rigorous evaluations.