An internationally renowned scholar shows that the Spanish Inquisition was originally the result of a long build-up of anti- Semitic racism for which the defense of Catholic orthodoxy was only a pretext. Within a few years of the 1391 pogroms in Spain, notes Netanyahu (The Marranos of Spain, not reviewed), conversions to Christianity reduced the country's Jewish community, the largest in the world, by nearly one third. Descendants of these converts, known as ``conversos'' (and pejoratively as Marranos, ``swine''), became a powerful elite; but following accusations that they were ``Judaizing,'' i.e., secretly observing Jewish rituals, the Inquisition was set up in 1480 to inquire into their Christian orthodoxy. Netanyahu confesses how his assumption that the conversos were Jewish martyrs was shattered when his reading revealed that they were bona fide Christians, bent on assimilation, who were regarded by other Jews as renegades and hated by their fellow Christians on account of their economic and political ascendancy. Beginning with an incisive overview of anti-Semitism in the pre-Christian world and in Christian Spain, Netanyahu shows how the Jews, as a defenseless alien minority, aligned themselves with the ruler and earned the hostility of the majority; and thus how, throughout the 15th century, the conversos were caught in a struggle between the king, their protector, and the rising power of the cities. We hear of the brilliant but unstable fortunes of the conversos under Juan II's chief minister, Alvaro de Luna, and how the ideologue Marcos Garc°a de Mora of Toledo developed a racial theory that was at odds with Church teaching and aimed at stopping the conversions. Netanyahu carefully analyzes the writings of conversos, such as Cardinal Juan de Torquemada (uncle of the notorious Inquisitor General), of their foes, and of allies, such as Alonso de Oropesa, General of the Hieronymite Order. Throughout, Netanyahu handles his vast material with confidence and sensitivity, not least when dealing with Church teaching. A vivid, magisterial resource for students of Spanish history and Jewish-Christian relations.