Humanae Vitae, the 1968 papal encyclical on contraception, unleashed a flood of argument about church teaching authority and the extent to which the pope and the Roman doctrinal congregation claim preeminent authority over the teaching of bishops and theologians. John P. Boyle presents here the first book length study that traces the historical and theological developments that produced official statements by the church about is own teaching authority and the assent owed to it, especially in the nineteenth and twentieth centuries.