Over the last few decades, 30 states and Washington, D.C., have enacted renewable portfolio standard (RPS) programs. These programs vary substantially, with most states having a restriction or preference with respect to whether renewables are located in-state or in-region. This Article takes a cross-disciplinary approach to analyzing these programs: first, by looking at how geographic limitations may run afoul of the dormant Commerce Clause (DCC); and second, by considering empirical research on how geographic provisions affect RPS programs’ cost-effectiveness.