Constance of Brittany (1161 – September 5 1201) was Duchess of Brittany between 1186 and 1196. Constance was the only child of Conan IV, Duke of Brittany and Earl of Richmond, by his wife Margaret of Scotland, countess of Hereford (granddaughter of king David II).

In 1181, Constance married Geoffrey Plantagenet, the fourth son of Henry II of England and Eleanor of Aquitaine, and had two children by him: Eleanor, Fair Maid of Brittany (1184-1241) and Arthur. Geoffrey assumed the title of Duke of Brittany and became the effective ruler of the duchy since the date. However, he died in 1186, stamped by a horse during a tournament. Constance then became ruler of Brittany until 1196, when she abdicated in favour of Arthur.

After her son's rebellion was quashed, Arthur disappeared into one of King John's castles, never to be seen again, and Eleanor was imprisoned for the rest of her days. King Henry had arranged for Constance to marry Ranulph de Meschines, 4th Earl of Chester in 1188, but this marriage was not successful, and Ranulph imprisoned his wife in 1196, an act that sparked a rebellion in her native Brittany. Finally in 1198 she was released, and had her marriage to Ranulph annulled. Constance then took Guy of Thouars as her husband, and by him was mother of Alix of Thouars, who married Peter de Dreux, first Breton ruler of the House of Dreux .

Constance lived out the last few years of her life quite peacefully, then died of leprosy in 1201, and was buried at the Villeneuve Abbey Church .

She has several very eloquent speeches on grief and death in Shakespeare's play King John.

See also: Dukes of Brittany family tree