This paper looks at the impact of the Pan-Islamic movement on nationalist politics and imperial policymaking in Mandatory Palestine. The study is built around three moments of tension between the colonial authorities and the country’s Islamic institutions: the controversy over the reintroduction of the Ottoman Sultan’s name in the Friday prayer (khutba) at the al-Aqsa mosque in October 1920; the convening of two international Islamic conferences by the Supreme Muslim Council in 1928 and 1931; and the decision by the mufti of Jerusalem to bury two prominent Muslim leaders, Sharif Husayn of Mecca and Muhammad Ali, one of the leaders of the Pan-Islamic Indian Khilafat movement, in the precincts of the Haram al-Sharif in 1931. Each moment raised fears for the Palestine government about the power of Pan-Islam to motivate Muslims to take action against the colonial state, while at the same time raising important questions among the Arab population about the place of Islam within the nationalist movement. For the colonial authorities, Pan-Islam threatened to radicalize Muslims from the outside; for Palestinian nationalists, Pan-Islam threatened to divert attention away from the Palestinian cause. In both cases, it was the transnational nature of Pan-Islam that represented a challenge to their vision of the country. Based on extensive research at the Israel State Archives, the Central Zionist Archives, the British National Archives, the British Library, and the Middle East Center Archives at St. Antony’s College, Oxford, this paper argues that while the threat of Pan-Islamism was exaggerated by the imperial authorities, particularly in the 1920s, it had a profound impact on the direction of Palestinian nationalism after the 1929 Western Wall Riots. Rather than building upon the momentum of the events of 1929 to push for a mass-based uprising against the British, I show how the mufti of Jerusalem, Hajj Amin al-Husayni, courted the support of Pan-Islamic groups in India, Egypt, and elsewhere for personal and institutional reasons. This would have a debilitating effect on Palestinian nationalism, dividing Muslims and Christians and alienating a younger generation of activists who demanded greater action from their nationalist leadership. The paper ends by considering how Pan-Islamism helped internationalize the Palestinian issue, tying the nationalist movement into a larger anti-colonial movement that was a precursor to the Third World Internationalism of the 1950s, while at the same time connecting British intelligence in Palestine into an empire-wide network of colonial surveillance of Islam.