Taking the métro is the most efficient way to get around Paris. Métro stations are recognizable either by a large yellow "M" within a circle or by the distinctive curly green Art Nouveau railings and archway bearing the full title (Métropolitain).
Sixteen métro and five RER (Réseau Express Régional, or the Regional Express Network) lines crisscross Paris and the suburbs, and you are seldom more than 500 yards from the nearest station. The métro network connects at several points in Paris with the RER, the commuter trains that go from the city center to the suburbs. RER trains crossing Paris on their way from suburb to suburb can be great time-savers because they make only a few stops in the city (you can use the same tickets for the métro and the RER within Paris).
It's essential to know the name of the last station on the line you take, as this name appears on all signs. A connection (you can make as many as you like on one ticket) is called a correspondance. At junction stations, illuminated orange signs bearing the name of the line terminus appear over the correct corridors for each correspondence. Illuminated blue signs marked sortie indicate the station exit. Note that tickets are valid only inside the gates, or limites.
Access to métro and RER platforms is through an automatic ticket barrier. Slide your ticket in and pick it up as it pops out. Keep your ticket during your journey; you'll need it to leave the RER system and in case you run into any green-clad ticket inspectors, who will impose a hefty fine if you can't produce your ticket (they even accept credit cards!).
Métro service starts at 5:30 am and continues until 12:40 am Sunday through Thursday, and until 2:15 am on Friday, Saturday, and nights before holidays, when the last train on each line reaches its terminus. Some lines and stations in Paris are a bit risky at night, in particular Lines 2 and 13, and the mazelike stations at Les Halles and République. But in general, the métro is relatively safe throughout, providing you don't travel alone late at night or walk around with your wallet hanging out of your back pocket.
All métro tickets and passes are valid not only for the métro but also for all RER, tram, and bus travel within Paris. Métro tickets cost €1.80 each; a carnet (10 tickets for €14.10) is a better value. The Carte Navigo system is the monthly and weekly subscription plan, with reusable cards available at most ticket windows; as of September 2015, there is one rate for all five zones. Receive a Pass Navigo Découverte for €5 plus the subscription for weekly (€21.25, valid Monday–Sunday) or monthly (€70, beginning the first of the month) service. Be sure to immediately attach a passport-size photo and sign your name. This magnetic swipe card allows you to zoom through the turnstiles and can be kept for years; just recharge it at any purple kiosk in the métro stations. Visitors can also purchase the one-day (Mobilis) and one- to five-day (Paris-Visite) passes for unlimited travel on the entire RATP network; both are valid starting any day of the week. Mobilis costs €7. Paris-Visite—which also gives you discounts on a few museums and attractions—costs €11.15 (one day), €18.15 (two days), €24.80 (three days), or €35.70 (five days).
RATP, which runs the city's public transport system, launched a dozen apps in late 2015, including "monRERA." It provides up-to-the-minute info on delays and travel times and can even tell you which end of the métro platform to stand on to facilitate the exit at your destination.
RATP. 3246; www.ratp.fr.