Debates over the original meaning of the establishment clause have usually revolved around the question of which broad church-state principle is represented by the clause. Strict separationists advocating a “wall of separation” highlight different historical evidence than do non-preferentialists who argue that the clause allows evenhanded government support for religion. A third group asserts that the clause was instead a federalism provision designed to reserve church-state decisions to the states. This chapter assesses these conflicting interpretations and concludes that the framers and the public understood the clause only as banning the establishment of a national church. That understanding did not necessarily represent an anti-establishment principle, however, and it assumed that church-state issues would continue to be resolved by the states. In light of the Supreme Court’s adoption of the incorporation doctrine, the combination of the federalism interpretation and the no-national-religion prohibition best encompasses the original constitutional decision.