Immigration detention is a growing threat to the well-being of migrants worldwide. While the use of this tool continues to increase, there is a growing consensus by governments on the need to pursue alternative programs. This paper examines the nature of these apparently contradictory developments and the reasons for tension in this area of migration policy. Drawing from research conducted by the International Detention Coalition and La Trobe University, this paper describes the Community Assessment and Placement (CAP) model, which seeks to prevent unnecessary detention, while allowing governments to meet the rationale offered for detention. It argues that the global trends of growth in detention and an increased emphasis on alternatives reflect competing political, policy and operational objectives. For example, governments wish to ensure compliance with deportation orders; alleviate political pressures regarding the harms associated with detention; and demonstrate control of territorial borders. Understanding the multiple rationales that shape this area of migration policy can help make sense of contradictory policy developments and identify the most effective ways to safeguard those who might be subject to detention.