This express train system runs underground in the city center and stretches far out into the suburbs. It can be a good time-saver if you are going from one side of Paris to the other, but access to platforms is often long and complicated, so it is not often worth it for a short trip. Metro tickets can be used for trips in central Paris, otherwise buy a ticket in advance. Keep it with you, as you have to slot it into a ticketmachine when you exit and enter the train.
You can prepare yourParis metroitinerary and get timetables. View maps of Paris metro, Paris buses, Paris RER and Paris Zones.