This article explores how the Palestine Liberation Organization (PLO) and its Research Center in Beirut appropriated classical Reform Jewish ideas to serve the PLO’s ideological battle against Zionism. How did PLO leaders and researchers learn in the 1960s of the Reform movement’s by-then long-overturned Pittsburgh Platform of 1885, and why did they think it still mattered? After noting a fascinating, if apparently unconnected, Late Ottoman precedent that may represent the starting point in the history of Palestinian Arab interest in Reform Judaism, the article identifies a more direct source of influence: the idiosyncratic twentieth-century American anti-Zionist Reform rabbi Elmer Berger. The article examines Berger’s collaboration with PLO intellectuals in challenging the legitimacy of Zionism. The article concludes with reflections on the broader question of how mutually hostile nationalisms relate to each other’s religious traditions and on the unexpected alliances fostered by debates over the nature of Jewishness.