More than 60,000 people are held in solitary confinement in U.S. prisons. This essay explores the ways in which solitary confinement is distinctive and yet also is a familiar feature of U.S. prisons. To do so, I track the expansion of solitary confinement, analyze the debate in federal courts about its lawfulness, and provide recent data on its widespread use. In 2005, the U.S. Supreme Court condoned the use of solitary confinement, even as it also licensed courts to inquire about whether a particular version imposed an “atypical and significant hardship” on an individual. If a prisoner can make such a showing, prison officials must provide some procedural buffers against arbitrary placements. Empirical understandings of the use of solitary confinement comes through nation-wide surveys undertaken by the Association of State Correctional Administrators and the Liman Center at Yale Law School. Data from 2018 identified more than 60,000 individuals who were placed in cells for 15 days or more for 22 hours or more. Almost 4,000 people have been so confined for three years or more. Solitary confinement is thus all too “typical” a facet of prison life. Yet its commonplace occurrence ought not insulate solitary confinement from the conclusion that it is an illicitly cruel practice that debilitates individuals. The complexity of doing so stems not only from the widespread use of solitary confinement, but also from the ways in which U.S. prisons are committed to many practices that are isolating and disabling of individuals.