Saʻadiah ben Yosef Gaon (b. Egypt 882/892, d. Baghdad 942) is a prominent rabbi, Jewish philosopher, and exegete of the Geonic period.

The first important rabbinic figure to write extensively in Arabic, he is considered the founder of Judeo-Arabic literature.

Known for his works on Hebrew linguistics, Halakha, and Jewish philosophy, he is one of the more sophisticated practitioners of the philosophical school known as the "Jewish Kalam" (Stroumsa 2003).

In this capacity, his philosophical work Emunoth ve-Deoth represents the first systematic attempt to integrate Jewish theology with components of Greek philosophy.

Saadia is also very active in opposition to Karaism, in defense of rabbinic Judaism.