The island lies approximately one kilometre (0.6 miles) off the country's north-western coast, at the mouth of the Couesnon River near Avranches and is 7 hectares (17 acres) in area. As of 2018, the island had a population of 30.

The commune's position —on an island just a few hundred metres from land— made it accessible at low tide to the many pilgrims to its abbey, but defensible as an incoming tide stranded, drove off, or drowned would-be assailants. The island remained unconquered during the Hundred Years' War.

The Mont-Saint-Michel abbey is an essential part of the structural composition of the town the feudal society constructed. On top, God, the abbey, and monastery; below this, the Great halls, then stores and housing, and at the bottom (outside the walls), fishermen's and farmers' housing. The abbey has been protected as a French monument historique since 1862.

Mont-Saint-Michel Bay
Mont-Saint-Michel Bay © Wikimedia

The Mont-Saint-Michel Bay has been named one of the world’s most beautiful bays, and was listed as a UNESCO world heritage site in 1979 for its aesthetic quality and its importance to the Christian tradition. Due to the significant tidal movements in this region (over 10 meters) a large part of the bay is uncovered at low tide. There are two granitic islands in the bay: Tombelaine and the Mont-Saint-Michel. Many birds and harbor seals live in this area.