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 twentieth ecumenical council of the Roman 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 the Lateran Councils, it met in the Vatican Basilica, hence its name of First Vatican Council. Its best-known decision is its definition of papal infallibility.

The Council was convoked to deal with the contemporary problems of the rising influence of rationalism, liberalism, and materialism. Its purpose was, besides this, to define the Catholic doctrine concerning the Church of Christ. There was discussion and approval of only two constitutions: the Dogmatic Constitution on the Catholic Faith and the First Dogmatic Constitution on the Church of Christ, the latter dealing with the primacy and infallibility of the bishop of Rome. The first matter brought up for debate was the dogmatic draft of Catholic doctrine against the manifold errors due to Rationalism.

The First Vatican Council took place in 1869 - 1870 and was the 20th of ecumenical councils recognized by Roman Catholicism.

The Second Vatican Council took place in the 1962 - 1965 and was the 21st.