SNCF Réseau is responsible for building and managing the railway infrastructure in France. It maintains tracks, signals, and stations, and coordinates train schedules and track access. You can think of it as the "landlord" of the rail network.

SNCF Voyageurs, on the other hand, operates the passenger trains that run on this infrastructure. It handles ticket sales, customer service, train staff, and the actual running of trains like TGV, TER, and Transilien.

Here’s how they work together:

SNCF Réseau builds and maintains the tracks; SNCF Voyageurs uses those tracks to run trains.

SNCF Réseau allocates time slots for train routes; SNCF Voyageurs requests those slots to plan its services.

SNCF Réseau ensures the infrastructure is safe and functional; SNCF Voyageurs ensures passengers get where they need to go.

SNCF Réseau coordinates with other rail companies; SNCF Voyageurs collaborates with Réseau to keep operations smooth.

Both are part of the larger SNCF Group and were separated into distinct entities to improve transparency and competitiveness in the French rail system.