During the past 20 years, super-maximum-security prisons have become a common feature of the corrections landscape in America. Yet little is known about the goals or unintended effects associated with these prisons. Even less is known about their causal logic--that is, how they achieve particular goals and impacts. The Urban Institute study involved a comprehensive review of literature, correctional agency documents, and media accounts; site visits to three states; interviews with 60 practitioners and policymakers; and a national survey of state prison wardens. This report summarizes the findings and their implications.