The NMBS (Dutch: Nationale Maatschappij der Belgische Spoorwegen) or SNCB (French: Société Nationale des Chemins de fer Belges) is the Belgian national railway operator. It was created in 1926. The NMBS/SNCB is an autonomous government company. In 2005, the company was split up into three parts: Infrabel, which manages the railway infrastructure, network operations and network access, the public railway operator NMBS/SNCB itself to manage the freight and passenger services, and NMBS/SNCB-Holding, which owns both public companies and supervises the collaboration between them. Essentially, this was a move to facilitate future liberalisation of railway freight and passenger services in agreement with European regulations. Several freight operators have since received access permissions for the Belgian network.

In 2004 the NMBS/SNCB carried 178,4 million passengers a total of 8676 million passenger-kilometres over a network of 3536 kilometres (of which 2950 km are electrified, mainly at 3000 volts DC and 351 km at 25 kV 50 Hz AC).

Tickets are relatively cheap and service frequent, in part due to the high population density, and in part to large government subsidies. The NMBS/SNCB is permanently updating its rolling stock.

The network currently includes two high speed lines suitable for 300 km/h traffic: HSL 1 runs from just south of Brussels to the French border, where it continues to Paris and Lille (and London beyond that), HSL 2 runs from Leuven to Liège. HSL 3 will run from Liège to the German border near Aachen and HSL 4 will connect with HSL-Zuid in The Netherlands to allow services to run from Antwerp to Rotterdam. HSL 4 and HSL 3 are currently under construction and will be ready in April 2007 and at the end of 2007 respectively. Both lines are equipped with ERTMS (ETCS level 2 + GSM-R, access and fall-back in level 1).