Jacob ben Asher, in Hebrew Ya'akov ben Asher, (1270-ca 1340) was an influential Medieval rabbinic authority. He is often referred to as the Baal ha-Turim ("Master of the Turim (Pillars)"), after his main work in halakha (Jewish law). He was the son of the Rabbi Asher ben Jehiel (known as the "Rosh"), a German-born Rabbi who moved to Spain. According to many, Jacob moved to Spain with his father and was not born there.

Jacob would succeed his father as the rabbi of the Jewish community of Toledo. Two of his brothers (Jehiel and Judah) were also rabbis of different communities in Spain. He lived in abject poverty most of his life.

His works include:

• Arba'ah Turim, a codex of Jewish law.
• A Torah commentary commonly referred to as "Baal ha-Turim". This commentary itself is prefaced by a brief commentary in itself, and this work has gained great influence to the point that it is printed in many one-volume Torah texts for synagogue use, only next to Rashi and the Targum of Onkelos. It contains mystical and symbolical references in the Torah text, often using gematria and acronyms as well as other occurrences of particular words elsewhere in the Torah.
• Kitzur Piskei ha-Rosh. A condensation of his father's Talmud commentary, focussing on the legal decisions reached.