Châtelet–Les Halles station is a major train hub in Paris and one of the largest underground stations in the world. Opened in 1977, it is the central transit hub for the Paris metropolitan area, connecting three of five RER commuter-rail lines and five of sixteen Métro lines. The hub hosts 750,000 travellers per weekday and platforms separated by up to 800 metres (0.5 mi). It is named after the nearby Place du Châtelet public square and Les Halles, the former wholesale food market of Paris, now a shopping mall.

The Réseau Express Régional, commonly abbreviated RER, is a hybrid commuter rail and rapid transit system serving Paris and its suburbs. It acts as a combined city-center underground rail system and suburbs-to-city-center commuter rail. In the city center, it acts as a faster counterpart of the Paris Métro, having fewer stops.