This report examines the social, economic, and demographic determinants of detention of refugees and migrants in Libya. Drawing on surveys of 5,144 refugees, migrants, and asylum-seekers, it compares the profiles and characteristics of those who reported being detained and those who did not in order to identify what factors make people on the move more likely to end up in detention. While the report focuses on the Libyan context, its findings have implications for understanding the drivers, dynamics, and consequences of migrant detention elsewhere.