Ouigo (French pronunciation: [wiˈɡo]) is a low-cost service range of both conventional and high-speed trains run by SNCF in France, and also to Belgium in cooperation with NMBS/SNCB.

Ouigo quickly proved popular with the travelling public, selling in excess of 2.5 million tickets during its first year of operation, and was rapidly expanded to cover more stations and regions.

In contrast to Europe's relatively liberalized airline market (open skies), the high-speed railways of many countries, including France, have traditionally been operated as a monopoly that is financed and owned by the respective national government.

[6] In an April 2013 interview with CNN Business Traveller, Pepy stated his hope for Ouigo was for it to be successful enough that it could be expanded and, eventually, provide services beyond France to the capitals of neighbouring countries, specifically naming Brussels, Amsterdam and London.

[8] In the few months between announcement and the commencement of passenger operators, Ouigo had reportedly sold 200,000 tickets while its website had been visited in excess of two million times.

SNCF stated that by 2020, its goal was for 25% of all high-speed passengers to travel aboard Ouigo services, which was set to expand its coverage to 30 destinations using its fleet of 34 trainsets.

Ouigo opted to charge more for tickets that board within central Paris rather than at Massy, Marne-la-Valley, or Roissy Charles de Gaulle Airport on the periphery of the city.

[19] On 6 July 2019, direct trains between Gare Montparnasse and Toulouse commenced, replacing a former TGV InOui service as well as marking the expansion of Ouigo into southwest France.

On 22 September 2020, SNCF announced via its Spanish subsidiary Rielsfera, that high-speed services in Spain would be launched during the following year as a part of its low-cost brand, using the name Ouigo España.

Both operations shared the same low-cost business model, with the new Classique services making intensive use of refurbished Corail coaches originally built for SNCF during the 1970s and 1980s.

[24] On 11 April 2022, the Ouigo Vitesse Classique service was launched, initially operating three trains per day along a pair of conventional lines that served a total of 14 stations.

Ouigo Train Classique serves three lines: From April 2022 to 15 December 2024: Domestic services use Corail cars, hauled by SNCF Class BB 22200 locomotives.

[34] The head of the rail division of the trade union CGT Bruno Charrier, referred to Ouigo as being a train service created for the poor.

However, since October 2013, the website has been changed to allow foreign customers to book tickets; the phone number is needed to provide information by text message for passengers in case of any issues.