Immigration enforcement in the United States has undergone a revolutionary transformation over the past three decades. Once episodic, border-focused, and generally confined to the efforts of a relatively small federal agency, immigration enforcement is now exceedingly well-funded and integrated deeply into the everyday policing of the interior United States. Not only are federal immigration agents more numerous and ubiquitous in the interior, but immigration enforcement has been integrated into the policing practices of state and local officials who once saw their purview as largely distinct from that of federal immigration enforcement agents. This essay briefly explains these developments, from shortly before the passage of the Immigration Reform and Control Act of 1986 through the present day, and assesses their consequences. It includes a brief discussion of the ways states and localities have responded to federal enforcement trends, whether through amplification or constraint.