8 U.S.C. § 1324 prohibits, among other activities, harboring aliens who enter the United States without authorization. In the more than six decades since the law was passed, federal courts’ understandings of what “harboring” means have varied. This Note argues that recent decisions in the Second and Seventh Circuits, both of which narrow the scope of liability for harboring, provide exemplary understandings of “harboring” and best comport with fundamental principles of criminal liability. This Note also examines the problems raised by state harboring statutes that track the language of 8 U.S.C. § 1324, arguing that after Arizona v. United States, state statutes that present even the potential for conflict with federal enforcement must be preempted. Together, redefining “harboring” and preempting state harboring statutes will promote a coherent and just federal immigration regime.