The Second Vatican Council (Latin: Concilium Oecumenicum Vaticanum Secundum, informally known as Vatican II) addressed relations between the Roman Catholic Church and the modern world. It was the twenty-first ecumenical council of the Catholic Church and the second to be held at Saint Peter's Basilica in the Vatican. The council, through the Holy See, formally opened under the pontificate of Pope John XXIII on 11 October 1962 and closed under Pope Paul VI on the Feast of the Immaculate Conception in 1965.