The Gare de Lyon, officially Paris Gare de Lyon, is one of the seven large mainline railway stations in Paris, France. It handles about 148.1 million passengers annually according to the estimates of the SNCF in 2018, with SNCF railways and the RER D accounting for around 110 million and the RER A accounting for 38 million, making it the second-busiest station of France after the Gare du Nord and one of the busiest in Europe.

RER D is one of the five lines in the Réseau Express Régional, a hybrid commuter rail and rapid transit system serving Paris and its suburbs. The 190-kilometre (120 mi) line crosses the region from north to south, with all trains serving a group of stations in central Paris, before branching out towards the ends of the line.