Camille Le Mercier d'Erm (1888 in Rennes – 1978 in Dinard) was a French poet, historian and Breton nationalist.
His work as a poet and historian is marked by nationalist claims and calls to rebellion against the French state on the model of Irish nationalism.
Le Mercier d'Erm also founded the activist journal Breiz Dishual (Free Brittany).
Immediately after the war, Le Mercier d'Erm helped to found a replacement journal, Breiz Atao (Brittany Forever), which was created in 1919.
He also continued to play a leading role among young Breton nationalist activists between the wars.