In many respects, Hamad al-Jasir (1908-2000) was the most prominent Saudi historian of the twentieth century. Yet despite the hundreds of news articles and scores of books he authored in his lifetime, little has been written in the academic literature about al-Jasir and his significance to modern Saudi political and social life. In 1980, after a lengthy and colorful career in education, journalism, and scholarship, al-Jasir embarked on what would become his most influential project, the documenting of the lineages of the tribes and families of Saudi Arabia. For the final two decades of his life, al-Jasir would devote much of his al-'Arab literary journal as well as several monographs to the recording of genealogical information about the kingdom’s inhabitants. Inside the high walls of his home in the al-Wurud neighborhood of Riyadh, al-Jasir stewarded a quiet revolution in modern Saudi consciousness, greeting hundreds of petitioners and inquirers who’d come to the Shaykh with genealogical queries or challenges to his documented findings. Al-Jasir’s turn to genealogical studies generated a tremendous amount of interest and controversy among Saudis, whose reactions are captured in the thousands of letters preserved in the scholar’s private library. While abridgments of some letters have been published in al-'Arab, many of these correspondences are unpublished and have never before been accessed by researchers. Hamad al-Jasir’s genealogical correspondences thus provide a rare and previously unexplored window into a Saudi society in the throes of rapid change. This paper will discuss the dominant themes that emerge from the correspondences, including the search for tribal belonging by non-tribal Saudis, the state’s uneasy relationship with tribalism, and the connection between genealogy and marriage patterns.