This chapter introduces the puzzles, questions, and concepts permeating the book, and provides an organizational map of its causal logic. It delineates the major challenges to the liberal state’s capacity to regulate immigration in an insecure international and domestic security environment. First, it identifies the perceived threats posed by human mobility and immigration. Second, the chapter describes the migration trilemma confronting policymakers whenever market imperatives and liberal immigrant policies are perceived to be in tension with their responsibility to safeguard public safety. Third, it reconceptualizes the regulatory politics of immigration within a context of various issue paradigms and threat perceptions. It offers a neo-institutional analytical framework linking diverse policy-making logics, actors, and norms within which these empirical developments can be explained over time. It proposes these dynamics illuminate the relationship between threat context and immigration regulation, and delimits the normative parameters of policy whenever security concerns preoccupy the public’s thinking.