Quas Primas (Latin: In the first) was an encyclical of Pope Pius XI. Promulgated on December 11, 1925, it introduced the Feast of Christ the King.
In 1925 Pope Pius XI asked Édouard Hugon, professor of philosophy and theology at the Pontifical University of Saint Thomas Aquinas, Angelicum to work on Quas Primas.
The encyclical summarizes both the Old Testament and the New Testament teaching on the kingship of Christ. Invoking an earlier encyclical Annum Sacrum of Pope Leo XIII, Pius XI connotes that the kingdom of Christ embraces the whole mankind.
Part of the encyclical symbolically marked that Christ must reign now temporally. In its replacing of the feast on the last Sunday of Pentecost, the later Mass of Paul VI calendar symbolized the new orientation of the Second Vatican Council in that Christ will reign, not now among nations, but at the end of time.