The Angelus (/ˈændʒələs/; Latin for "angel") is a Catholic devotion commemorating the Incarnation of Christ. As with many Catholic prayers, the name Angelus is derived from its incipit—the first few words of the text: Angelus Domini nuntiavit Mariæ ("The Angel of the Lord declared unto Mary"). The devotion is practised by reciting as versicle and response three Biblical verses narrating the mystery, alternating with the prayer "Hail Mary". The Angelus exemplifies a species of prayers called the "prayer of the devotee".

The devotion is traditionally recited in Roman Catholic churches, convents, monasteries and by the faithful three times a day: in the morning, at noon and in the evening (usually just before or after Vespers). The devotion is also observed by some Western Rite Orthodox, Lutheran, and Anglican churches.

The Angelus is usually accompanied by the ringing of the Angelus church bells, which is a call to prayer and to spread goodwill to everyone. The angel referred to in the prayer is Gabriel, a messenger of God who revealed to the Virgin Mary that she would conceive a child to be born the Son of God (Luke 1:26–38). In Eastertide, the Angelus is replaced by the Regina Coeli.

According to Herbert Thurston, the Angelus originated with the 11th-century monastic custom of reciting three Hail Marys at the evening, or Compline, bell.

The first written documentation stems from the Italian Franciscan friar Sinigardi di Arezzo (died 1282). Franciscan friaries in Italy document the use in 1263 and 1295. The current form of the Angelus prayer is included in a Venetian Catechism from 1560. The older usages seem to have commemorated the resurrection of Christ in the morning, his suffering at noon, and the annunciation in the evening. In 1269, St Bonaventure urged the faithful to adopt the custom of the Franciscans of saying three Hail Marys as the Compline bell was rung.

The Angelus is not identical to the "noon bell" ordered by Pope Calixtus III (1455–58) in 1456, who asked for a long midday bell-ringing and prayer for protection against the Turkish invasions of his time. In his 1956 Apostolic Letter Dum Maerenti Animo about the persecution of the Catholic church in Eastern Europe and China, Pope Pius XII recalls the 500th anniversary of the "noon bell", a prayer crusade ordered by his predecessors against what they considered to be dangers from the East. He again asks the faithful throughout the world, to pray for the persecuted Church in the East during the mid-day Angelus.^{[citation needed]}

The custom of reciting it in the morning apparently grew from the monastic custom of saying three Hail Marys while a bell rang at Prime. The noon time custom apparently arose from the noon time commemoration of the Passion on Fridays. The institution of the Angelus is by some ascribed to Pope Urban II, by some to Pope John XXII in the year 1317. The triple recitation is ascribed to Louis XI of France, who in 1472 ordered it to be recited three times daily. The form of the prayer was standardised by the 17th century.

The manner of ringing the Angelus—the triple stroke repeated three times, with a pause between each set of three (a total of nine strokes), sometimes followed by a longer peal as at curfew—seems to have been long established. The 15th-century constitutions of Syon monastery dictate that the lay brother "shall toll the Ave bell nine strokes at three times, keeping the space of one Pater and Ave between each three tollings". The pattern of ringing on Irish RTÉ Radio One and television, RTÉ One, consists of three groups of three peals, each group separated by a pause, followed by a group of nine peals, for a total of eighteen rings.