Régis-Marie-Joseph de l'Estourbeillon de la Garnache (11 February 1858 - 7 September 1946) was a Breton aristocrat and politician who was associated with Breton regionalist activism. He is generally known as Régis de l'Estourbeillon, but held the title Marquis de l'Estourbeillon. He was born in Nantes. He became interested in preserving Breton regional identity as a young man, founding the Breton Regionalist Union in 1898. He edited La Revue de Bretagne with the Count René de Laigue. The publication appeared from 1902 to 1943. He died at the château de Penhoët, Avessac.