Isadore Twersky (also known as Yitzhak Asher Twersky, October 9, 1930 – October 12, 1997) was an Orthodox rabbi and Hasidic Rebbe, and university professor who held the position as Nathan Littauer Professor of Hebrew Literature and Philosophy at Harvard University, a chair previously held by Harry Austryn Wolfson.

He was especially known as an international expert in the writings and influence of the 12th-century Jewish legalist and philosopher Maimonides, and Abraham ben David, the Rabad of Posquieres.

Much of his Torah knowledge was acquired through private study under the tutelage of his father Meshullam Zushe Twersky (his predecessor as the Talner Rebbe of Boston) and his future father-in-law Joseph B. Soloveitchik, rather than through formal yeshiva instruction (Hacker 2005).

Upon his graduation from Harvard, he began studies toward a doctorate in Near Eastern Languages and Civilizations, under the guidance of the scholar of medieval philosophy, Harry Austryn Wolfson.

Twersky's lectures in the synagogue on Tuesday nights and late Saturday afternoons were known for their erudition and originality, in the tradition of elite religious Torah study, with the vocabulary and worldliness of a Harvard historian.

[2] The Twerskys' elder son Mosheh, a rabbi and lecturer at Yeshivas Toras Moshe, was murdered in the 2014 Jerusalem synagogue attack.

His popular course, Moderation and Extremism, which compared and contrasted the paths to virtue in the works of Aristotle, Maimonides, and Thomas Aquinas, drew over 200 students in 1995, the final year it was taught.