R. Isaac ben Abraham of Posen (d. 1685), rabbi and author. Isaac was a pupil of Jonah Teomim and Abraham Meir of Bar. He was on friendly terms with the kabbalist Moses Zacuto. His first position was as rabbi in Lutsk. In 1664 he was appointed rabbi of Vilna and from there he went to Posen in 1667. His extensive knowledge of the Talmud and Kabbalah earned him the title of R. Isaac the Great, his opinion on halakhic questions being frequently sought by contemporary scholars (cf. Magen Avraham to Sh. Ar., OH, 1:7; 32:35; Gaon Zevi of Zevi Hirsch Horowitz (Prague, 1737), 2a–3a). His novellae are mentioned in Sha'arei Shamayim of Jehiel Michael ha-Levi (Prague, 1675), 94b; in Lev Aryeh of Judah Aryeh Hotchke (Wilhelmdorf, 1674—on the weekly portion Toledot), 16a; Leket Shemu'el of Samuel Feivush Katz (Venice, 1694); and in Even ha-Shoham u-Me'irat Einayim of Eliezer Goetz b. Meir (Dyhernfuerth, 1733), nos. 11 and 48. Part of his responsa collection was published under the title Be'er Yizhak (Vienna, 1894), and part of the remainder was published at the end of R. Asher b. Jehiel's commentary to Sukkah (1903). The whole collection of responsa was in the possession of R. Spira of Munkacs. R. Isaac died in Posen.