During the years surrounding the 1967 war, the Balfour Declaration was the subject of significant debate and polemics by PLO intellectuals, especially those affiliated with the PLO Research Center in Beirut. Why did the PLO find the Declaration still relevant half a century after it was issued, and what do the particular arguments these PLO intellectuals used to challenge the Declaration tell us about how they understood their predicament in the 1960s and early 1970s? This article addresses these broader questions in four parts. (1) It considers the prominent place of the Balfour Declaration in the PLO’s founding covenant and proposes an explanation for why the critique of the Declaration is linked to the denial of Jewish nationhood. (2) Through an examination of several Research Center publications, it offers a précis of the substantive arguments articulated by PLO intellectuals concerning the Declaration in these critical years and notes the dissonance between two particular lines of argument: rejecting the Balfour Declaration because the British had already promised Palestine to the Hashemites (in the Hussein-McMahon correspondence of 1915–16) and rejecting the Declaration because the British had no right to promise Palestine to anyone. (3) In light of the complex, evolving, and ever-tense relationship between Palestinian nationalists and the Hashemite regime, and considering other contemporaneous writings about the Hashemites by the PLO Research Center director, the article tentatively suggests that these intellectuals may well have been aware of the dissonance between their arguments, and perhaps intentionally unsettled the legitimacy of a regime that, not unlike Israel, was established partly as a consequence of a World War I–era promise. (4) By exploring in closer detail one argument that distinguished the Balfour Declaration from the Hussein-McMahon correspondence, the article considers the place of international law and pan-Arabist thought in the PLO intellectuals’ arguments.