Legal scholarship lacks a comprehensive account of the theoretical underpinnings of immigration law. This Article attempts to fill that void by identifying four theories to explain various aspects of immigration law and the arguments advanced in support of such law: (1) individual rights theory, which turns on the prospective migrant’s right of entry into the United States, (2) domestic interest theory, which considers whether and to what degree allowing migrants into the United States will benefit the country as a whole, (3) national values theory, which focuses on whether the admission of migrants promotes the fundamental values of the country, and (4) global welfare theory, which considers how immigration decisions at the domestic level affect the political, social, and economic makeup of the global community. This Article argues that the universe of theoretical arguments must be employed to evaluate immigration policy proposals. This conceptual approach: (1) untangles the range of justifications that support immigration proposals, (2) explains why political actors with disparate practical and ideological interests may coalesce around a particular policy prescription, and (3) clarifies how a law can achieve greater traction by either engaging the dominant theoretical perspective or utilizing multiple theoretical underpinnings. Ultimately, this Article creates a new means for analyzing immigration law—one that will help scholars, politicians, and the public to evaluate immigration reform efforts.