Erispoe (died 2 or 12 November 857) is Duke of Brittany from 851.

After the death of his father Nominoe, he leads a successful military campaign against the Franks, culminating in his victory at the Battle of Jengland.

He is subsequently referred to as "King of Brittany", but this indicates only that he received a gift of regalia and not that he was ever king by imperial grant or even in his own charters.

Erispoe's recorded titles include provinciæ Brittaniæ princeps, dux Brittonum, and rex tyrannicus Brittonum.

The last means "tyrant [ie usurping] king of Brittany", but if Erispoe was usurping regality in Brittany at that time (857) it is not attested in other sources.

It may imply continued Frankish resentment of the title.

He is called rex Brittonum by Regino of Prüm.