Jacob ben Nissim ibn Shahin was a Jewish philosopher and mathematician who lived in Kairouan, Tunisia, in the 10th century; he was a younger contemporary of Saadia.
At Jacob's request, Sherira Gaon wrote a treatise entitled Iggeret, on the redaction of the Mishnah.
Jacob is credited with the authorship of an Arabic commentary on the Sefer Yeẓirah (translated into Hebrew by Moses ben Joseph).
In the same introduction Jacob speaks of Galen, repeating the story that that celebrated physician was a Jew named "Gamaliel."
Jacob ben Nissim wrote a work on Indian mathematics under the title Ḥisab al-Ghubar (Hebrew: האבק חשבון).