Today in countries across the globe, immigration-related detention has become an established policy apparatus that counts on dedicated facilities and burgeoning institutional bureaucracies. Before the decade of the 1980s, however, detention appears to have been largely an ad hoc tool, employed mainly by wealthy states in exigent circumstances. This paper details the history of key policy events that led to the diffusion of detention practices during the last 30 years and assesses some of the motives that appear to have encouraged this phenomenon. The paper also endeavors to place the United States at the centre of this story because its policy decisions were instrumental in initiating the process of policy innovation, imitation, and—in many cases—imposition that has helped give rise to today’s global immigration detention phenomenon. More broadly, in telling this story, this paper seeks to flesh out some of the larger policy implications of beyond-the-borders immigration control regimes. Just as offshore interdiction and detention schemes raise important questions about custody, accountability, and sovereignty, they should also spur questions over where responsibility for the wellbeing of migrants begins and ends. As this paper demonstrates, when it comes to immigration detention, all the answers cannot be found just at home.