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Mont Saint-Michel (English: St Michael's Mount) is a rocky tidal island in Normandy, France. It is located approximately one kilometer off the country's north coast, at the mouth of the Couesnon River near Avranches.

Mont Saint-Michel was used in the sixth and seventh centuries as an Armorican stronghold of Romano-Breton culture and power, until it was ransacked by the Franks, thus ending the trans-channel culture that had stood since the departure of the Romans in AD 460.

Before the construction of the first monastic establishment in the 8th century, the island was called Mont Tombe. According to legend, the archangel Michael appeared to St. Aubert, bishop of Avranches, in 708 and instructed him to build a church on the rocky islet. Aubert repeatedly ignored the angel's instruction, until Michael burned a hole in the bishop's skull with his finger.

The mount gained strategic significance in 933 when William "Long Sword", Duke of Normandy, annexed the Cotentin Peninsula, definitively placing the mount in Normandy. It is depicted in the Bayeux Tapestry, which commemorates the 1066 Norman conquest of England. Ducal patronage financed the spectacular Norman architecture of the abbey in subsequent centuries.

In 1067, the monastery of Mont Saint-Michel gave its support to duke William of Normandy in his claim to the throne of England. It was rewarded with properties and grounds on the English side of the Channel, including a small island located at the west of Cornwall, which, modelled after the Mount, became a Norman priory named St Michael's Mount of Penzance.

During the Hundred Years' War the English made repeated assaults on the island but were unable to seize it, partly due to the abbey's improved fortifications. Les Michelettes, two wrought-iron bombards left by the English in their failed 1423–24 siege of Mont Saint-Michel, are still displayed near the outer defense wall.

The wealth and influence of the abbey extended to many daughter foundations, including St Michael's Mount in Cornwall. However, its popularity and prestige as a centre of pilgrimage waned with the Reformation, and by the time of the French Revolution there were scarcely any monks in residence. The abbey was closed and converted into a prison, initially to hold clerical opponents of the republican régime. High-profile political prisoners followed, but by 1836 influential figures, including Victor Hugo, had launched a campaign to restore what was seen as a national architectural treasure. The prison was finally closed in 1863, and the mount was declared a historic monument in 1874. The Mont Saint-Michel and its bay were added to the UNESCO list of World Heritage Sites in 1979, as they rank very high on such World Heritage Site criteria as cultural, historical, and architectural significance, as well as human-created and natural beauty.