RER C

Line C was opened on 26 September 1979, following the construction of a new 1-kilometre (5⁄8 mi) tunnel connecting the Gare d'Orsay railway terminus (now Musée d'Orsay) with the Invalides, terminus of the Rive Gauche line to Versailles, along the banks of the Seine. Services operated between Versailles-Château-Rive-Gauche – Invalides – Quai-d'Orsay, branching to Massy – Palaiseau, and Juvisy – Dourdan / Saint-Martin d'Étampes. At that point the line was named the Transversal Rive Gauche.

In May 1980, service was extended to Saint-Quentin-en-Yvelines – Versailles – Chantiers – Gare des Invalides. The RER C designation was then introduced, replacing the Transversal Rive Gauche name from this point onwards.

On 25 September 1988, the VMI ("Vallée de Montmorency – Invalides") branch to the north-west opened. This branch mostly used the infrastructure of the "ligne d'Auteuil" (incorporated into the "ligne de petite ceinture" from 1867, closed to passengers from 22 July 1934), and a new 3-kilometre (2 mi) tunnel connection between Batignolles and Saint-Ouen, connecting to the RER C's main trunk at Champ de Mars-Tour Eiffel via a curved bridge (the only one in Paris) over the Seine river. That extended services to Montigny – Beauchamp and Argenteuil.

The station Porte de Clichy, located between Pereire – Levallois and Saint-Ouen, opened on 29 September 1991. In 1992, the line was extended from Juvisy to Versailles. A further 9 kilometres (5+5⁄8 mi) extension from Montigny – Beauchamp to Pontoise was opened on 28 August 2000. On the same day a new station, Bibliothèque François Mitterrand, opened in order to create a new connexion with Métro Line 14, located between Paris-Austerlitz and Boulevard Masséna, which was closed and replaced by the new station. Another new station, Saint-Ouen-l'Aumône-Liesse, opened on 24 March 2002.

On 27 August 2006, the C3 service (between Ermont–Eaubonne and Argenteuil) was transferred to the Transilien Paris – Saint-Lazare suburban rail network as Line J.

On 16 December 2006, Boulevard Victor was renamed Boulevard Victor – Pont du Garigliano to highlight the new interchange with tramway line T3.

In February 2012, the Versailles – Rive Gauche station was renamed Versailles-Château-Rive-Gauche, to highlight its proximity to the Palace of Versailles, and to avoid confusion with other stations in Versailles served by RER C.

In December 2023, the C8 branch was withdrawn. The new Transilien Line V began a shuttle service between Versailles-Chantiers and Massy-Palaiseau. The line between Savigny-sur-Orge and Massy-Palaiseau became tram-train line T12 Express.

Like all other RER lines in Paris, the mission code, or the name of service, consists of four letters. The names of services are displayed on trains and on passenger information display systems. The four-letter code begins with a letter that corresponds to the train's terminus.^[4][5] For example, trains displaying NORA terminate at Pontoise because NORA starts with the letter 'N' (and codes that start with the letter 'N' indicate the destination of Pontoise).

Several services had the code name changed in 2015, for example KUMA to KYVI.^[6]

The extension of the Saint-Quentin-en-Yvelines branch to Coignières station, with intermediate stops at Trappes and La Verrière, was included in Phase 1 (2013-2020) of the Schéma directeur de la région Île-de-France (SDRIF) adopted by the Regional Council of Île-de-France on September 25, 2008.^[8] However, this vital project to serve the Saint-Quentin-en-Yvelines conurbation (improved service to La Verrière and Trappes stations, and control of (high) ridership at Saint-Quentin-en-Yvelines - Montigny-le-Bretonneux station) has been delayed^[9] due to the high infrastructure costs involved, estimated at over €120 million at June 2008 economic conditions.^[10] The project requires work to be carried out on the line to make the Trappes crossing safer. The project is now expected to be completed around 2030.