Since the late 1990s, greater demand has been placed on local and state jurisdictions to enforce immigration laws. To a large extent, this pressure was exerted through the federal government’s increased use of enforcement programs that rely on state and local law enforcement cooperation. These programs have drawn heavy criticism, and some communities across the country have responded to such pressure by adopting ordinances that explicitly limit such cooperation. These ordinances, colloquially known as “sanctuary policies,” have been the subject of a growing body of academic literature. This chapter provides a review of the literature on so-called “sanctuary policies” by focusing on their definition, history, factors that explain their adoption, and the association (or lack thereof) between “sanctuary” policies and crime. Our review reveals the existence of nuances in the definition of “sanctuary” cities and policies. Historically, such policies have been a response to changes in federal immigration enforcement efforts. In some cases, “sanctuary” policies are strictly defined as local efforts aimed at limiting cooperation with federal enforcement, in others, as preconditions for immigrant inclusion at the local level. Additionally, our review finds no evidence that these policies constitute a magnet for “criminal aliens,” insofar as there is no association between presence of “sanctuary” policies and violent crime.