This article presents the findings of the first research study of the Institutional Hearing Program (IHP), a prison-based immigration court system run by the U.S. Department of Justice. Although the IHP has existed for four decades, little is publicly known about the program’s origin, development, or significance. Based on original analysis of archival records, this study makes three central contributions. First, it traces the origin and growth of the IHP within federal, state, and municipal correctional facilities. Notably, although the IHP began in 1980 as a program to deport Cuban asylum seekers held in civil detention in an Atlanta prison, it now operates to deport noncitizens serving prison sentences in twenty-three federal prisons, nineteen state prison systems, and a few municipal jails. Second, this article uncovers the crucial role that prison-based immigration courts have played in shaping the design of carceral institutions around the priorities of an immigration system that primarily targets Latinos for deportation. Third, this article shows how immigration courts embedded in carceral spaces have served as influential, yet overlooked, incubators of changes to immigration law and practice that today apply to all immigration courts, not just the IHP. These findings have important implications for contemporary understandings of the relationship between immigration detention, racialized control of migration, and penal punishment.