Over the last twenty-five years, immigration detention policies and practices have proliferated around the globe. We look at four liberal democratic countries with the largest immigration detention systems—Australia, Canada, the United Kingdom, and the United States—and identify components of an immigration detention policy ‘package’ as well as historical parallels in the early adoption of detention in these countries. This ‘Anglo model’ of detention is based on three main features: (1) the existence of indefinite and/or mandatory immigration detention policies; (2) the use of private security actors and infrastructure; and (3) the use of creative legal geographies in order to interdict and detain people offshore. Past scholarship on detention has focused on single national case studies or assumed the leadership of the US as the primary innovator in the field. Our paper establishes the empirical and theoretical grounds for considering these countries as a group and suggests a more complex process of policy adoption among them. Identifying an Anglo model of detention lays the critical groundwork for understanding the expansion of immigration detention and the transnational diffusion of detention policies among these countries, as well as where and how countervailing pressures to detention might form.