Second Vatican Council

The Second Ecumenical Council of the Vatican, or Vatican II, was the twenty-first Ecumenical Council of the Roman Catholic Church. An Ecumenical Council is a meeting of the bishops of the Church to discuss matters of Church doctrine and practice. Pope John XXIII started Vatican II in 1962 and it lasted until 1965, when Pope Paul VI ended it. Four future popes took part in the council's opening session: Cardinal Giovanni Battista Montini, who on succeeding Pope John XXIII took the name of Paul VI; Bishop Albino Luciani, the future Pope John Paul I; Bishop Karol Wojtyła, who became Pope John Paul II. Father Joseph Ratzinger, who was only 35 at the time, was there as a theological consultant. More than forty years later, he became Pope Benedict XVI. 
Different things were discussed. These aimed at modernising the church, and opening a dialogue with other religions. Many people see these meetings as the most important event in the Catholic Church in the 20th century. They let Mass be said in different languages, instead of just Latin.