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. He authored Creative Judaism (1941), The Ethics of Toleration Applied to Religious Groups in America (1941), Judaism Under Freedom (1956), What We Mean by Religion (1958), Varieties of Jewish Belief (1966), and Reconstructing Judaism: An Autobiography (1986).