The RER A is a rapid transit line in the Île-de-France region of France, part of the Réseau Express Régional system. It connects central Paris to various suburbs, including Marne-la-Vallée, where Disneyland Paris is located. The line is known for its high passenger volume and serves both commuters and tourists. The RER A operates on a mix of underground and above-ground tracks, with several key stations such as Châtelet-Les Halles and La Défense. It is an essential part of the public transport network, providing efficient access to major business districts and attractions in the region.