By Metro & Regional Trains
A century old, the Paris Metro is one of the most modern and efficient in the world. Recently some 200 of the system's nearly 300 stations were refurbished. The Metro is the easiest and most efficient way to get around Paris. Most stations display a map of the system at the entrance. Within Paris, you can transfer between the subway and the RER regional trains for no additional cost. To make sure you catch the right train, find your destination, and then visually follow the line it's on to the end of the route and note its name. This is the sign you look for in the stations and the name you'll see on the train. Transfer stations are known as correspondances (note that some require long walks -- Chatelet-Les Halles is the most notorious).

Few trips will require more than one transfer. Some stations have maps with push-button indicators that'll help you plot your route by lighting up when you press the button for your destination.

Metro fares to outlying suburbs on the Sceaux, the Noissy-St-Leger, and St-Germain-en-Laye lines cost more and are sold on an individual basis depending on the distance you travel. At the entrance to the Metro station, insert your ticket into the turnstile and pass through. Take the ticket back, because it may be checked by uniformed police officers when you leave the subway. There are also occasional ticket checks on the trains, platforms, and passageways. If you're changing trains, get out and determine which direction (final destination) on the next line you want, then follow the bright orange CORRESPONDANCE signs until you reach the proper platform. Don't follow a SORTIE sign, which means "exit." If you exit, you'll have to pay another fare to resume your journey.
The Paris Metro runs daily from 5:30am to 1:15am, at which time all underground trains reach their final terminus at the end of each of their respective lines. Be alert that the last train may pass through central Paris as much as an hour before that time. The subways are reasonably safe at any hour, but beware of pickpockets.

By Bus
Bus travel is much slower than the subway. Most buses run from 7am to 8:30pm (a few run until 12:30am, and 10 operate during the early morning hours). Service is limited on Sundays and holidays. Bus and Metro fares are the same and you can use the same carnet tickets on both. At certain stops, signs list the destinations and numbers of the buses serving that point. Destinations are usually listed north to south and east to west. Most stops along the way are also posted on the sides of the buses. To catch a bus, wait in line at the bus stop. Signal the driver to stop the bus and board. Most bus rides (including any that begin and end within Paris's 20 arrondissements and nearby suburbs) require one ticket. For bus travel to some of the more distant suburbs, an additional ticket might be required. If you intend to use the buses a lot, pick up an RATP bus map at its offices at place de la Madeleine, 8e (Metro: Madeleine), or 54 quai de la Rapee, 12e (Metro: Gare de Lyon), or at any tourist office.