Opponents of—and sometimes advocates for—sanctuary policies describe them as obstructions to the operation of federal immigration law. This premise is flawed. On the better view, the sanctuary movement comports with, rather than fights against, dominant new themes in federal immigration law. A key theme—emerging both in judicial doctrine and on-the-ground practice—focuses on maintaining legitimacy by fostering adherence to equitable norms in enforcement decision-making processes. Against this backdrop, the sanctuary efforts of cities, churches, and campuses are best seen as measures necessary to inject normative (and sometimes legal) accuracy into real-world immigration enforcement decision-making. Sanctuaries can erect front-line equitable screens, promote procedural fairness, and act as last-resort circuit breakers in the administration of federal deportation law. The dynamics are messy and contested, but these efforts in the long run help ensure the vindication of equity-based legitimacy norms in immigration enforcement.