This book examines the implementation of immigration policy in Mexico through an ethnographic and relational lens, focusing on the subjectivities of state officials. Based on three years of qualitative research (2017–2019) conducted at the Siglo XXI Migration Station in Tapachula, Chiapas—Mexico’s southern border with Guatemala—the study explores how agents of the National Institute of Migration (INM) experience, interpret, and enact state power at the local level. The analysis foregrounds the subjective dimensions of bureaucratic work—emotions, fears, desires, and forms of reasoning—and their direct impact on migrants’ experiences of detention and deprivation of liberty. Central to the book is an examination of the institutional processes of subjection that produce subjects in immigration detention. Approaching immigration policy as a political, cultural, and social practice embedded in everyday institutional life, the study shows how state institutions are sustained not only through legal frameworks and administrative procedures, but also through relational processes of power that shape subjectivities. In this framework, both state agents and migrants are constituted as subjects through power, albeit in profoundly unequal ways. Drawing on a biopolitical perspective, the book analyzes how the regulation and control of bodies are enacted within an institution that, while formally situated within administrative law, operates in practice through policing and carceral logics. The findings reveal that immigration agents themselves are shaped by institutional processes of subordination and depoliticization, which in turn contribute to the routine reproduction of practices of humiliation, contempt, and domination toward detained migrants within an asymmetric configuration of power. This book will be a valuable resource for criminologists, sociologists, and anthropologists engaged with questions of immigration and state power. It will also be useful to policymakers and practitioners working with migration governance and border control.