The practice of imprisoning Jews in ghettos and marking them out with special signs (as was introduced by Pius vi in the Papal States, inter alia, in 1775) is associated more with the Nazism of the Third Reich than with the Roman Catholic Church. Nevertheless, the Church maintained its policy of perfidis Judaeis until the beginning of the 1960s, when it was stopped by Vatican ii, probably because of the pressure of social and political factors. This topic is, however, difficult to explain, often very controversial, and subject to many different interpretations. Here we show that anti-Semitic ideas were present in the Church before Vatican ii, and that they have a religious, theological, and philosophical background. We discuss those interpretations which, in an ideological sense, connect anti-Semitism in the Church with the genocidal anti-Semitism of the Third Reich. This article underlines the revolutionary change in the Church’s attitude toward Jews in Vatican ii, a change caused primarily by the Holocaust.