This article is the result of a first-hand exploration of the relevance of the Cairo Genizah as a source for Intellectual history of the Middle Ages. It is not only significant for understanding Jewish thought, previously documented in numerous studies, but also to the Islamic world. Whereas S.D. Goitien’s oeuvre and the groundbreaking work of his disciples widely demonstrated the importance of Genizah documents as historical sources on the Mediterranean region, the relevance of its Islamic/Arabic literature is less often acknowledged. This topic will be addressed in the light of my doctoral research, which examined the legacy of dream interpretation preserved in Genizah fragments of dream books written in Judeo-Arabic during the pre-modern period. After a brief introduction to the history of dream books—manuals for dream interpretation—in the Near East, and to the epistemology of Jewish and Islamic dream interpretation, the main findings of the research will be listed and summarized. Finally, in a detailed case study, a synoptic edition of texts representing the Taʿbīr al-ruʾyā, a brief dream manual attributed to al-Kirmānī, demonstrates the importance of Cairo Genizah manuscripts to the literary history of the composition.