  Joseph Albo (c. 1380–1444) was a Jewish philosopher active in Christian Spain in the first half of the fifteenth century. His theoretical work found expression in his well-known opus Sefer ha-‘Ikkarim [Book of Principles], completed in 1425 in the town of Soria in the crown of Castile. In this work, Albo addresses a wide variety of interpretive, theological and philosophical issues, in a style integrating logical, methodical analyses with exegetical discussions. Albo’s composition reveals his exposure to the works of many Jewish philosophers that preceded him, particularly Maimonides, Hasdai Crescas (Albo’s teacher in his formative years), and his contemporary, Simeon ben Zemah Duran. The historical circumstances in which he functioned, especially the Catholic Church’s persecution of the Jews in Christian Spain, led him to contribute to the anti-Christian polemic, and apparently also permitted his exposure to the writings of such Christian philosophers as Thomas Aquinas.