A striking series of events of the past two decades have tended to raise questions about the exercise of teaching authority in the Catholic Church. The Second Vatican Council, the Encyclical Humanae Vitae, the controversy over Hans Kung's book on infallibility and the subsequent declaration of Rome that he could no longer teach as a Catholic theologian, the colloquium to which Edward Schillebeeckx was summoned by the Vatican, the pastoral letter of the American bishops on the question of nuclear warfare have a stimulated a lively discussion of the claims of the Catholic hierarchy to authoritative magisterium.