Rabbi Ira Eisenstein (November 26, 1906 – June 28, 2001) was an American rabbi who founded Reconstructionist Judaism, along with Rabbi Mordecai Kaplan, his teacher and, later, father-in-law through his marriage to Judith Kaplan, over a period of time spanning from the late 1920s to the 1940s. Reconstructionist Judaism formally became a distinct denomination within Judaism with the foundation of the Reconstructionist Rabbinical College in 1968, where he was the founding president.