After 9/11, the Bush administration and, to a lesser degree, the Obama administration authorized controversial interrogation, detention, trial, lethal targeting, and surveillance practices. At the same time, American officials frequently invoked legal norms to justify these policies. This chapter introduces the book’s central questions: how can we make sense of these attempts to legalize human rights abuses and how does law influence state violence? As initially outlined in this chapter, the book argues that national security legal cultures shape how political actors interpret, enact, and evade legal rules. In the global war on terror, a culture of legal rationalization pushed American authorities to construct plausible legality, or legal cover for contentious counterterrorism policies. This culture contrasts with cultures of exception and cultures of secrecy, which have shaped American national security practice in the past, as well as a culture of human rights favored by many international law and human rights advocates.