The peninsula in northwest France that was historically the region of Brittany is Brittany.
Brittany projects into the Atlantic between the English Channel and the Bay of Biscay. Its coastline, rugged headlands and maritime position helped give the region a distinctive identity within France. In French, the region is called Bretagne, while its inhabitants are known as Bretons.
Brittany was an independent duchy for much of the Middle Ages before being united with France in 1532. Its Celtic heritage reflects migration from Britain during the early medieval period, and Breton remains a minority Celtic language alongside French.
A common mix-up is Normandy, which lies immediately east across the Cotentin area and is associated with the Norman Conquest and D-Day. Provence and Aquitaine are historical regions in southeastern and southwestern France, respectively, not the northwestern peninsula.