This article summarizes some of the negative psychological effects of imprisonment. It examines the psychological stressors—dehumanization, deprivation, and danger—to which prisoners are exposed, and the process of prisonization by which they attempt to accommodate to their conditions of confinement. It also discusses the effects of two opposite prison extremes, overcrowding and solitary confinement, as well as the kind of vulnerabilities that many prisoners bring to prison that make the experience a form of retraumatization for them. The article ends with a set of brief, programmatic but psychologically informed proposals for change.