This is the first English translation of one of the most important treatises written during the late-Middle Ages in defense of converts from Judaism, favoring religious tolerance in the face of religious and racially motivated prejudice and violence. The book also includes a fresh Latin edition, drawing on all known manuscripts. The text was written in response to the actions of the "Old Christians" of Toledo against the "New Christians," also called conversos, in 1449. A letter of Pope Nicholas V favouring the converts is included.