Transilien (pronounced [tʁɑ̃siljɛ̃]) is the brand name given to the commuter rail and tram-train network operated by SNCF and serving Île-de-France, the region surrounding and including the city of Paris.

The Transilien brand was established on 20 September 1999 as a way to unify the suburban network that existed since the late nineteenth century.

Its immediate success led to the creation of numerous lines, primarily intended to link the main cities of France.

Suburban service has long been marginal for large companies, with the exception of the West, where several short lines crossing residential areas are seeing their local traffic increase sharply.

The successive topographic maps of the French IGN show the urbanization of the Parisian suburbs over the decades near the stations of the suburban lines.

In the region, especially south of the capital, these lines follow the bottom of the valleys because the steam traction did not support the steep gradients: the urbanization of the trays takes place later with the advent of the automobile for the general public during the second half of the 20th century.

The bad memories of these difficult years, and the individual transports' multiplication reduced the traffic, with regression from 1946 to 1958, and an even worse situation between 1952 and 1958.

From 1959 to 1969, major electrification began the gradual modernization of the rail network, with the final disappearance of steam engines in the suburbs in 1970.

RER Line A experienced a spectacular increase in passengers, which leads to a saturation point in less than ten years.

However, despite the numerous investments made over the past three decades, the suburban network suffered from a poor public image and bad decision making by local authorities.

While the RATP benefited from the RER's image, which it is generally associated with, having an aura of modernity and innovation under a distinct logo, the SNCF network reminded people of suburban trains which often had a negative connotation of obsolete rolling stock, chronic delays, and unwelcoming train stations.

All vehicles received a new blue and gray Transilien livery with panels of color to highlight doors and internal characteristics.