family associated with an ancient lordship in the Île-de-France (Montfort-l'Amaury); this lordship first became famous in French and English history because of its association with members of the family, which held it in the 13th century; it was transmitted to a junior branch of the Capetian house of Dreux, which furnished dukes of Brittany in the 14th–15th century.

Montfort-l'Amaury took its name from Amaury, or Amalric (d. c. 1053), the builder of the castle there, whose father had been invested with the lordship by Hugh Capet. Amaury's grandson Simon (d. 1181 or later) married Amicia, ultimately the heiress of the English earldom of Leicester, and it was through their son, the crusader Simon de Montfort (Montfort, Simon de) (q.v.), that the family first attained real prominence. By his wife Alice de Montmorency he left four sons: Amaury de Montfort (see below), who succeeded to Montfort-l'Amaury and to his father's titles in Languedoc; Simon de Montfort (Montfort, Simon de, Earl Of Leicester) (q.v.), who became earl of Leicester and played a major role in English affairs; Guy de Bigorre (d. 1220); and Robert (d. 1226).

Amaury de Montfort (d. 1241), defeated in war, lost all his rights in Languedoc to King Louis VIII (1229) and was compensated with the office of constable of France (1231). Captured by the Muslims in the Holy Land (1239), he was released in 1241 but died at Otranto in Apulia on his way home.

Guy (d. 1228), who was with his brother at Zara and in Syria, also took a large part in the Albigensian crusade, receiving the fiefs of Rabastens and St. Antonin. He ceded his rights in Languedoc to the French crown in 1226.

John de Montfort (d. 1249), Amaury's son and successor, left only a daughter, Beatrice (d. 1312), who was married in 1259 to Count Robert IV of Dreux. Their daughter Yolande (d. 1322) was married first, in 1285, to Alexander III of Scotland and second, in 1294, to Arthur II of Brittany, to whom she brought the Montfort lands. Their son John de (John (IV)) Montfort (d. 1345), whose elder brothers accorded him only the Montfort title, contested the duchy of Brittany with Charles of Blois; and his son was recognized duke of Brittany, as John IV, by the Treaty of Guérande (1365). Thenceforward he and his descendants John V (John V (or VI)) (q.v.; d. 1442), Francis I (d. 1450), Peter II (d. 1457), Arthur III (d. 1458; see Richemont, Arthur, constable de), and Francis II (q.v.; d. 1488) constituted the House of Montfort as dukes of Brittany. But Francis II left only an heiress, Anne Of Brittany (q.v.; d. 1514). Her marriages to Charles VIII and Louis XII of France were followed by the marriage of Claude (her daughter by Louis) to King Francis I; this union secured the Montfort possessions to the French crown.