The Cairo Geniza, alternatively spelled Genizah, is a collection of some 400,000 Jewish manuscript fragments and Fatimid administrative documents that were kept in the genizah or storeroom of the Ben Ezra Synagogue in Fustat or Old Cairo, Egypt. These manuscripts span the entire period of Middle-Eastern, North African, and Andalusian Jewish history between the 6th and 19th centuries CE, and comprise the largest and most diverse collection of medieval manuscripts in the world.

The Genizah texts are written in various languages, especially Hebrew, Arabic and Aramaic, mainly on vellum and paper, but also on papyrus and cloth. In addition to containing Jewish religious texts such as Biblical, Talmudic and later Rabbinic works (some in the original hands of the authors), the Genizah gives a detailed picture of the economic and cultural life of the Mediterranean region, especially during the 10th to 13th centuries.

Manuscripts from the Cairo Geniza are now dispersed among a number of libraries, including the Cambridge University Library, the Jewish Theological Seminary of America, the John Rylands Library, the Bodleian Library, the University of Pennsylvania's Katz Center for Advanced Judaic Studies, the British Library, the Hungarian Academy of Sciences, the National Library of Russia, Alliance Israélite Universelle, and multiple private collections around the world. Most fragments come from the geniza chamber of the Ben Ezra Synagogue, but additional fragments were found at excavation sites near the synagogue and in the Basatin cemetery east of Old Cairo. Modern Cairo Geniza manuscript collections include some old documents that collectors bought in Egypt in the latter half of the nineteenth century.