 The scientific-philosophical Arabo-Islamic encyclopedia bearing the title Epistles of the Brethren of Purity and of the Lovers of Faith (Rasa’il ikhwan al-safa’ wa-khullan al-wafa’), which includes 52 treatises about mathematical sciences, logic, physical sciences, metaphysics, anthropology, and theology, had a relevant, although unexpected and not usually studied influence on Medieval Judaic thought in the 11th-15th centuries in Spain and Provence, and in Yemen as well.