This dissertation examines the link between territory and personhood that underpins contemporary system of immigration and border control. It consists of four independent chapters that investigate how immigration law constructs the “alien” as a governable subject. Both territory and personhood are conceptualized here as the outcomes of processes of partition, which classify land and human life through political and juridical categories. Borders enclose land, and they link inert soil to territorial qualities, thus giving a spatial extent to sovereignty. Personhood bestows political life on bodily matter, thus making citizens and aliens out of human bodies. The chapters examine the relations between these two processes as they unfold in contemporary legal-geographic systems of immigration control. From these premises, the research question that guides this dissertation is rather simple: who is the alien? After the introduction, the first two chapters approach this question while examining two distinct legal systems. The second chapter focuses on US immigration law, which is described as a system that classifies the alien population across statuses, with each status being interpreted as a legal-geographic location that expresses a specific degree of foreignness within the country. The third chapter examines alternative conceptualizations of the relation between territory and life by focusing on human rights law, and specifically on the jurisprudence of the European Court of Human Rights. The last two chapters abandon an exclusively legal focus to investigate the US system of immigration detention. The fourth chapter introduces this topic by examining the geographic literature concerning detention and incarceration, while the fifth and final chapter describes an episode of political resistance inside a US immigration detention center during the Covid-19 pandemic. The final contribution closes the dissertation by describing the attempt to subvert the legal-geographic system that was previously analyzed in the second chapter. In its totality, the dissertation advances a legal-geographic analysis that focuses on the spatial structures that are inherent to contemporary systems of immigration control. Through an engagement with the philosophic literature on biopolitics, I argue that geographers are uniquely positioned to contribute to the study of the relation between law and life by highlighting the spatial dynamics that inform said relation. I utilize space as a material, discursive, and metaphoric concept that illuminates the necessity to thinking through space when confronting complex systems of power and control.