Reform of the Roman Breviary by Pope Pius X

The reform of the Roman Breviary by Pope Pius X was promulgated by that Pope with the apostolic constitution Divino afflatu of 1 November 1911. The Roman Breviary is the title of the book obligatorily used for celebrating the Roman Rite Divine Office from the revision of Pope Pius V (apostolic constitution Quod a nobis, 9 July 1568) to that by Pope Paul VI (apostolic constitution Laudis canticum, 1 November 1970).

Source: Wikipedia — Reform of the Roman Breviary by Pope Pius X (CC BY-SA 4.0)