Les Sables-d'Olonne is a seaside resort and port situated on the Atlantic coast of Western France within the Vendée department of the Pays de la Loire region. It functions as a subprefecture and an administrative commune, ranking as the second most populated municipality in the department after La Roche-sur-Yon. Geographically, the town lies between La Rochelle and Saint-Nazaire, near the coastal terminus of the A87 highway which connects it to La Roche-sur-Yon, Cholet, and Angers. The nearest major metropolitan area is Nantes, located approximately 105 kilometers to the north by road.

The settlement was founded in 1218 from Havre d'Olonne by Savary I de Mauléon, who served as the Lord of Mauléon and Sénéchal of Poitou. Louis XI separated Les Sables-d'Olonne from the town of Olonne in 1472, improving the harbor and fortifying its entrance. It grew to become France's largest cod-fishing port with 14,000 inhabitants in the seventeenth century. On January 1, 2019, the communes of Olonne-sur-Mer and Château-d'Olonne merged with Les Sables-d'Olonne, retaining the latter name for the expanded administrative entity.

The town features significant historical architecture including the Tour d'Arundel, a fifteenth-century tower surrounded by fortifications near the harbor. The Phare de l'Armandèche stands as the last major lighthouse built in France, constructed in 1968 on a wild part of the coastline. A notable local feature is L'Île Penotte, a street where houses are decorated with mosaics made from seashells. The area also includes the Musée de l'Abbaye Sainte-Croix, a municipal museum housed in a seventeenth-century building devoted to modern and contemporary art.

Les Sables-d'Olonne is best known as the starting and finishing point of the round-the-world Vendée Globe yacht race, which occurs every four years. The town hosts the Vendée Air Show on La Grande Plage beach and is home to Zoo des Sables, featuring around fifty species. The local tourism industry traces its roots to bathing establishments begun in 1825. The city also serves as the setting for Georges Simenon's 1948 novel Les Vacances de Maigret and is the birthplace of pirate François l'Olonnais.

The population was recorded at 49,603 as of 2023. The climate is oceanic with an average annual temperature of 13.2 °C and rainfall of 746.7 mm. Transport access includes a high-speed train station with direct services from Paris, Nantes, and La Roche-sur-Yon. The nearest international airports are Nantes Airport, located 119 kilometers to the northeast, and La Rochelle–Île de Ré Airport, situated 58 kilometers to the southeast. The town offers extensive rail connections and road access via the A87 highway.