Abbaye Notre-Dame de Langonnet, Cistercian abbey in Langonnet, France

Abbaye Notre-Dame de Langonnet is a former Cistercian abbey whose buildings are arranged around a square courtyard. A tall square tower with a round clock face and a tapering pointed roof rises at the junction of two wings; the walls facing the courtyard have rows of arched windows and a ground-floor arcade of round arches. The chapter house dates from the 13th century, and the church was dedicated in 1789.

Founded on 20 June 1136 by Conan III, Duke of Brittany, and his mother Ermengarde of Anjou, the abbey received twelve monks from L'Aumône Abbey in Loir-et-Cher. It was devastated during the War of the Breton Succession and rebuilt between 1470 and 1518 by abbots Vincent and Henri de Kergoët. Most of the present buildings date from 1650–1780, and the church was dedicated in 1789.

The abbey's name comes from Notre-Dame, and its church was dedicated in 1789 by abbot François Chevreul. Since 1857 it has belonged to the Congregation of the Holy Spirit, whose missionaries ran a secondary school and novitiate here by 1880. On 7–8 August 1880 the relic of Saint Maurice's right humerus was transferred here from Carnoët before 20,000 devotees.

The abbey lies southeast of Langonnet village on the Plouray road, in the Gourin deanery. It is still run by the Congrégation du Saint-Esprit, so parts of the complex are not open to the public; ask at the entrance which areas can be visited. The chapter house, in ogival style, dates from the 13th century.

Napoleon I established the stud farm by decree on 10 June 1806, with forty stallions and ten brood mares. General Baron de Wimpfen objected in a report of 28 May 1807, calling Langonnet "the most appalling desert of Lower Brittany" and noting supplies could only be had at Pontivy or Hennebont. By 1843 the depot held seventy stallions.