This chapter describes the new field of ‘border criminology’, which examines the growing convergence between criminal justice and immigration control. It starts with an overview of the global immigration context before outlining key ideas and areas of scholarship within border criminology. It then turns to look more closely at penal power, drawing on fieldwork and policy analysis to explore the methodological and epistemological implications for criminology of examining citizenship and migration. It ends by arguing for greater engagement with the challenges and effects of mass mobility. As the impact of a decision to arrest in any street in Britain may be felt in countries far away, it is time for criminologists to take into account more explicitly the global nature of criminal justice and reflect on its implications for how and what we study.