The Second Vatican Council was the largest council of the Church, beginning under John XXIII in October 1962 and running for four sessions until 1965, ending on the Feast of the Immaculate Conception under Paul VI. It reaffirmed and proclaimed the timeless teaching of the Church, though it did not define much new doctrine, the pastoral thrust was very important. We must follow the instruction of all ecumenical councils, even a council that does not define doctrine. The interpretation of this council can be seen through the Catechism of the Catholic Church, which has many references to council documents.
Two foreign words dominated the council, Aggiornamento ("bringing up to date") and Ressourcement ("going back to the sources"). Both complement each other, as without returning to the sources, we cannot be sure what we are bringing up to date, and without bringing the teaching on those sources up to date, we may be stuck in a 16th-century mindset. Various factions vied for more and less of each at the council, but the reforming element prevailed.
Some of the major theologians who influenced the council were Karl Rahner, Yves Congar, Edward Schillebeeckx, Hans Küng as well as Karol Wojtyła (later John Paul II). Many of these major reformers formed the board of the journal Concilium, but in 1974, Henri de Lubac, Hans Urs von Balthasar, and Joseph Ratzinger (later Benedict XVI), concerned by some of Concilium's editors' desire for more reforms after Vatican II and not through the Church, formed a rival journal, Communio.
This conflict between those who wanted more reform outside the Church
and those who wanted to come to consensus on the council first would
continue for many years.