Papal supremacy is the doctrine of the Catholic Church that the Pope, by reason of his office as Vicar of Christ, the visible source and foundation of the unity both of the bishops and of the whole company of the faithful, and as pastor of the entire Catholic Church, has full, supreme, and universal power over the whole church, a power which he can always exercise unhindered: that, in brief, "the Pope enjoys, by divine institution, supreme, full, immediate, and universal power in the care of souls."

Pastor aeternus was issued by the First Vatican Council, July 18, 1870. The document defines four doctrines of the Catholic faith: the apostolic primacy conferred on Peter, the perpetuity of the Petrine Primacy in the Roman pontiffs, the definition of the papal primacy as a papal supremacy, and Papal infallibility – infallible teaching authority (magisterium) of the Pope.