The union of the Duchy of Brittany with the Crown of France was the culmination of a political process begun at the end of the 15th century in the wake of the Mad War. It resulted in the Edict of Union of 13 August 1532 and the incorporation of the duchy into the Crown lands of France, a critical step in the formation of modern-day France.

The House of Rohan is a Breton family of viscounts, later dukes and princes in the French nobility, coming from the locality of Rohan in Brittany. Their line descends from the viscounts of Porhoët and is said to trace back to the legendary Conan Meriadoc. Through the Porhoët family, the Rohans are related to the Dukes of Brittany, with whom the family intermingled again after its inception. During the Middle Ages, it was one of the most powerful families in the Duchy of Brittany. The Rohans developed ties with the French and English royal houses as well, and they played an important role in French and European history.