The Theatines, officially named the Congregation of Clerics Regular (Latin: Ordo Clericorum Regularium; abbreviated CR), is a Catholic order of clerics regular of pontifical right for men founded by Archbishop Gian Pietro Carafa on 14 September 1524.
 The order was founded by Saint Cajetan (Gaetano dei Conti di Thiene), Paolo Consiglieri, Bonifacio da Colle, and Giovanni Pietro Carafa (afterwards Pope Paul IV). Carafa was Bishop of Chieti; Chieti (Theate) is a city of the Abruzzi in Central Italy, from which the congregation adopted its specific name, to distinguish it from other congregations (Barnabites, Somaschi, Caracciolini, etc.) modelled upon it. The Theatines combined the pursuit of evangelical perfection traditional among religious orders with apostolic service generally expected of diocesan clergy. It was Carafa who wrote the constitutions of the order.
 Cajetan consecrated his order to the Cross, which he adopted as its emblem, and the foundation took place on the feast of the Finding of the Holy Cross, 3 May 1524. It was approved on 24 June of that year, by Pope Clement VII in the Brief Exponi Nobis. On 14 September, feast of the Exaltation of the Holy Cross, Cajetan and his companions made solemn profession before the papal altar of St. Peter's Basilica in Rome, in the presence of Mgr. Giovanni Battista Bonziano, Bishop of Caserta, a special papal delegate. Carafa was chosen the first General.
 The chief object of the order was to recall the clergy to an edifying life and the laity to the practice of virtue.  They founded oratories (among them the celebrated Divino Amore) and hospitals, devoted themselves to preaching the Gospel, and reformed lax morals. They were exclusive, aristocratic, and formidably austere. They wore the simple black cassock of the local clergy and maintained a modest lifestyle.
 The prohibition on both owning property and soliciting alms tended to limit applicants from members of the aristocracy, and so they remained relatively few in number. In 1546 they were briefly joined with the Somaschi Fathers, but as the object of the respective orders differed, they separated in 1555. In 1527 their house in Rome was sacked by the army of Charles V, and the Roman community sought refuge in Venice.
 They founded many churches, among them the Sant'Andrea della Valle in Rome, a gift of Costanza Piccolomini D'Aragona, Duchess of Amalfi. This church is a masterpiece of Carlo Maderno and contains several paintings by Domenichino. The Theatines still operate the church.
 In France, through the efforts of Cardinal Mazarin, they built the Church of St. Anne la Royale opposite the Louvre in 1644. In Spain, under Philip II, the Theatine Cardinal Paolo Burali d'Arezzo, filled various embassies at the command of the viceroy of Naples. In Portugal, John IV, in 1648, gave the Theatines a splendid house and college for the education of noble youth. In England, under Henry VIII, Thomas Goldwell, Bishop of St. Asaph, entered the order of Theatines. In Bavaria, the Theatine Church St. Kajetan was built from 1663 to 1690, founded by Elector Ferdinand Maria.
 The Theatines were the first to found papal missions in: Golconda (in present-day India), Ava (Burma), Peru, Mingrelia (Georgia), founded by Andrea Borromeo, the East Indies, (the history of which was written by the Theatine Bartolomeo Ferro - "Missioni Teatine nelle Indie Orientali"), Arabia, and Armenia. In 1626 Theatines went to Persia.
 Theatine manuscripts dating from 1530 until the end of the 18th century show there were missions established in a number of other countries. By 1700 the Theatines numbered 1400.
 By the end of the eighteenth century, decline had set in, exacerbated by political upheavals. General suppression of religious orders affected the Theatines more significantly because the order historically acquired no possessions and so had no institutional infrastructure.
 Pope Pius X had a hand in attempts at revival, calling upon the services of Cardinal José de Calasanz Félix Santiago Vives y Tutó. The papal Motu Proprio Auspicato, of 15 December  1909, decreed the union of the Congregation of the Regular Theatine Clergy with the youthful Spanish Congregation of the Holy Family founded at Barcelona by Josep Manyanet y Vives, but the two groups were separated again in 1916. In 1910, the Theatines were amalgamated with the Congregation of Saint Alphonsus Liguori, which had been founded in Mallorca in 1867.
 According to the Annuario Pontificio, as of 31 December 2014, the Theatines had 34 houses and numbered 170 members, of whom 139 were priests. The Theatines are present in Argentina, Brazil, Colombia, Mexico, the Netherlands, Spain, and the United States of America, where they maintain a mission at Durango, Colorado.
 The Order has numbered among its members:
 It has also furnished one pope, Paul IV (Giovanni Pietro Carafa), 250 bishops, archbishops, and papal legates, and several cardinals.
 Among noted nineteenth-century Theatines was the Sicilian Father Gioacchino Ventura dei baroni di Raulica,  a philosopher, littérateur, and orator. One of his most celebrated works is his funeral oration on the death of Daniel O'Connell. The astronomer Giuseppe Piazzi (1746-1826), professor of mathematics and astronomy in Palermo, Sicily, discoverer of the first asteroid, Ceres, in 1801, became a Theatine at the age of 19.