Super-maximum security prisons were rare just 20 years ago but today over two-thirds of States house over 20,000 inmates in “supermax” correctional facilities. In the face of mounting criticisms regarding the high costs of supermax prisons and the notion that confinement within them is unconstitutional and inhumane, it is necessary to examine the stated goals of supermax prisons, how the goals are achieved, and the unintended outcomes associated with the goals. Urban Institute researchers undertook a systematic review of the research literature, corrections agency reports, and news and legal accounts of supermax prisons. Data also included site visits to 3 States, interviews with 60 corrections leaders in 11 States, and national survey data collected from wardens. A benefit-cost analysis (BCA) policy brief and tool was also created using data from practitioners and researchers. Results of statistical analyses indicated considerable differences regarding the stated and perceived goals of supermax prisons, although the national warden survey data indicated vast agreement about four critical goals: increasing safety, order, and control throughout the prison system and incapacitating violent or disruptive inmates. The logic by which these prisons seek to achieve their goals is unclear and there are a wide range of unintended effects of supermax prisons, such as an increase in inmate mental illness, many of which remain contentious. States have yet to conduct benefit-cost analyses of their supermax prisons and it thus remains unclear whether the benefits of supermax prisons outweigh their high costs. Future research should examine inmate outcomes upon release from supermax prisons, such as success gaining housing and employment and integrating back into the community. References, appendixes, tables