Rabbi Yeshaya Siff has served as the spiritual leader of the Young Israel Synagogue of Manhattan since 1964. He concurrently held the Schottenstein Family Chair as Associate Professor of Talmud at Yeshiva University until retiring in 2007.

Rabbi Siff was ordained at the Rabbi Isaac Elchanan Theological Seminary in 1956. He is a magna cum laude graduate of Yeshiva College and earned a Master of Arts Degree in Midrashic Literature at the Bernard Revel Graduate School of YU.

Prior to assuming the pulpit at the Young Israel Synagogue of Manhattan, Rabbi Siff had been a chaplain in the United States Army and the spiritual leader of the Stern College for Women Synagogue where he met his wife Rita nee Markovitz. They are the parents of five married children.

Rabbi Siff is a founding member and past president of the United Jewish Council of the Lower East Side, a member of the boards of Ezras Torah and Mesivtha Tifereth Jerusalem and a member of the Rabbinical Council of America. His work has been published in Halachic journals.