Second Vatican Council
The Second Ecumenical Council of the Vatican, commonly known as the or , addressed relations between the Catholic Church and the modern world. The council, through the Holy See, was formally opened under the pontificate of Pope John XXIII on 11 October 1962 and was closed under Pope Paul VI on the Solemnity of the Immaculate Conception on 8 December 1965.
First Vatican Council
The First Vatican Council () was convoked by Pope Pius IX on 29 June 1868, after a period of planning and preparation that began on 6 December 1864. This, the twentieth ecumenical council of the Catholic Church, held three centuries after the Council of Trent, opened on 8 December 1869 and adjourned on 20 October 1870. Unlike the five earlier general councils held in Rome, which met in the Lateran Basilica and are known as Lateran councils, it met in the Vatican Basilica, hence its name. Its best-known decision is its definition of papal infallibility.