The French rail system (SNCF) is extensive and very efficient. We often use it to get from Paris to the beginning of our walk and back again at the end.
The TGV (high-speed train) network is more expensive than normal trains (Intercités and TERs), but saves time and is quite an experience.
To book a train ticket on the SNCF network, go to the Oui.sncf website. Oui.sncf is the on-line travel agency of SNCF.
When buying your tickets you are given the choice of an eticket (to print at home or to save on your mobile), or a hard copy ticket sent to you by mail.
Booking in advance gives you the option of buying a “prem” ticket. Prems are much cheaper and, if available, are listed in green in the “Non exchangeable” ticket column.
They can be purchased from about three months before travel, but there are only a limited number available on each train, so book early.
If the tickets for your train are not yet on sale, you can subscribe to receive an email notification when they become available.
An oddity of the French rail system is that tickets (but not etickets) must be “composted” before boarding the train.
This means getting them punched in a little yellow machine at the entrance of the platform.
Tickets are always checked by a conductor on the train and if they are not composted, you will be frowned upon, or even fined.