Isabella of Brittany (French: Isabelle; 1411 – c. 1444) was a daughter of John V, Duke of Brittany, and his wife, Joan of Valois. Isabella was a member of the House of Dreux.
Isabella's maternal grandparents were Charles VI of France and Isabeau of Bavaria. Her paternal grandparents were John IV, Duke of Brittany and Joan of Navarre.
Isabella was related to three Queens of England. Two of her maternal aunts, Isabella of Valois and Catherine of Valois were queens of England and after the death of her paternal grandfather, John IV, her grandmother, Joan, became queen of England by her marriage to Henry IV of England. Isabella of Valois was married to Henry's predecessor, Richard II of England. Catherine of Valois was married to Henry IV's son, Henry V of England.
On 1 October 1430, at Redon, Isabella married Guy XIV de Laval. Guy fought in many different battles in the Hundred Years' War and fought alongside Joan of Arc. Guy had been betrothed to Isabella's younger sister, Margaret, who died before the marriage could take place, so Guy married Isabella instead.
Isabella and Guy had three sons and seven daughters:
Isabella died around 1444, and she is buried in Nantes. Her husband remarried after her death, to Françoise de Dinan, widow of Isabella's younger brother Gilles, Lord of Chantocé. Her husband was buried at the collegial church of Saint-Thugal at Laval.
This family tree shows Isabella's paternal side of her family, her mother and brothers. It shows that after the death of her brothers, her uncle, Arthur became Duke of Brittany.