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.

The noble Breton family line of Porhoët was a French noble family in the middle ages, from around 990 through the 1200's. Notable members included Odo I, Odo II, and Alan I. Alan I would go on to form the Franco-Breton House of Rohan, which survives to the modern day.