The RER Trains in Paris connect to the Metro Train stations in Paris and also the TGV and conventional long distance trains (Grandes Lignes)
The long distance trains are often TGV Trains (high speed) the conventional trains often serve shorter trips between cities.
Buying Train Tickets
For the RER, Metro, and TGV trains it is possible to book ahead to save. You can buy same day tickets at the station or you can buy day passes or week long passes for Metro and RER. You can buy the tickets at automated ticket vendors throughout the station. The automated systems accept credit cards (not American Express)
Lines at ticket sales counters can be long in the afternoon.
Certain days and destinations can sell out on the high speed trains so it is a good policy to book ahead. Seats are asssigned on TGV trains. Second Class seats can sell out early on popular destinations.
Paris RER trains are an underground and surface rail system used by commuters and visitors to travel to the suburbs, outlying towns, and CDG Airport.
The RER trains connect to the Metro at several stations and they connect to the conventional and TGV long distance trains. The 5 RER train lines are designated by color codes and alphabet letters A to E.
The lines are also numbered according to their destination or final stop. The Charles De Gaulle Airport line is blue, B3 at the airport and blue, B4 at the other end in St Remy-les-Chevreuse, for instance.
The Blue, B, RER line runs from CDG Airport in the northeast through the center of Paris to the southwestern suburbs and beyond. This RER line stops at over 30 stations on its course through the center of Paris. Those stops include Notre Dame and Luxembourg in the center of Paris.
Find your way by using the name of the final destination, Charles de Gaulle for instance, (northeast of Paris) and then finding your desired stop, (Notre Dame, for instance for the Latin Quarter.)
If you are coming from the Charles de Gaule to the Notre Dame station, note that you will travel towards St Remy-les-Chevreuse . Find the correct platform in this manner and You will travel south toward Notre Dame.
The Paris RER operates in a maze of tunnels and peope movers that include the Metro tunnels. You can connect to different Metro lines (color coded and numbered) or RER lines, (color coded and alphabetized) within the many stations. You must follow the color codes and numbers (blue 3, for instance, for Charles de Gaulle Airport) to find your way. The stations do not offer elevators or escalators (some do) so you should travel lightly. Travel with smalll change to buy tickets in the automated machines. 1.70 Euro for entry (scroll the automated vendor menu for English and other languages)