Papal infallibility means the pope is never wrong when he speaks or acts ex cathedra -- on behalf of the Church as its leader, in religious and spiritual matters. This is a privilege the pope inherits, according to the First Vatican Council (1869-1870), because "he is empowered, through the divine assistance promised him by blessed Peter, with that infallibility with which the Divine Redeemer willed to endow the Church." (This does not mean the pope is perfect, or omniscient or personally infallible, as is often misinterpreted.)