This article examines how increasingly punitive prison conditions, epitomized by the birth and spread of the supermax prison, developed in the United States. This analysis builds on a growing literature about the “new punitiveness” of U.S. punishment policy and its global proliferation. This article shifts the focus away from the policies that have led to increasing rates of incarceration, however, and toward the policies that have shaped the conditions of incarceration. Drawing on archival research and more than 30 oral history interviews with key informants, I examine the administrative and legislative processes that underwrote the supermax innovation in California in the 1980s. During California's late twentieth‐century prison‐building spree, prison administrators deployed multiple rhetorics of risk to extend their control over conditions of confinement in state prisons. As the state invested billions of dollars in prison building initiatives, legislators, who were focused primarily on building prisons faster, ceded authority over prison design and conditions to prison administrators. In the end, rather than implementing legislative policy, prison administrators initiated their own policies, institutionalizing a new form of “supermax” confinement, pushing at the limits of constitutionally acceptable practices.