The most comprehensive public transportation option in Paris, France is the Métro. Without it, Paris would grind to a halt-and does every time there is a transport strike. The Paris Métro, which dates back to 1900, is laid out on a grid of 16 lines similar to other European public transportation systems like the London Underground and the Barcelona Metro, so that every line reaches every area of the city within a couple of blocks. You can get single tickets as well as day or week passes, or even special passes like the Museum Pass that gains you access both to the Métro and over 60 museums in Paris.
Be careful, though, since the Paris Métro is divided into five zones and the more zones you buy for, the more expensive your ticket or pass. But once you are in the Métro system, you can transfer to any line inside of it without paying more. Expect a lot more security inside the Métro post-9/11, including paired security guards with dogs. Awareness of the vulnerability of public transportation to terrorists, always high in Europe, has gone up since the bombings in London and Madrid.
Zones 1-3 are the center of Paris, including famous areas like Notre Dame, the Louvre and the Eiffel Tower. Zone 5 is technically outside the city and includes attractions like Versailles. If you’re up for a relatively cheap day trip, you can either get a Zone 5 ticket or get a package ticket that includes a round trip to Versaille and back as well as the price of entrance, all discounted.
The Métro also intersects with the RER (Réseau Express Régional), which goes into Zone 5 and out into the country. Most of the RER was built in the 1960s and 1970s to provide regional service to the Parisian suburbs. All public transportation systems in Paris, including the Métro, RER and city busses, come under the RATP (Régie Autonome des Transports Parisiens).
You can get a bus service from the Orly or Charles de Gaulle airports into Paris. These cost about $20 one-way, but are still cheaper than taking a taxi or an airport shuttle, which costs 27 € one-way (about $34). City bus services also exist along similar routes to the Métro. You can get on them at signs along the street. However, the Métro is so popular and extensive that the city bus system is relatively less used, at least by travelers.
Travelers may want to try out a city tour bus. Open tour busses travel around the center of Paris, commenting on the various sites as well as the history of the city. You can get on and off anywhere on the route. It’s a slow, but good, way of getting a passing glance of Paris in general, with the option of getting off for a closer look. You might also try a water taxi Batobus along the Seine.
Also available are the usual private big city options, including taxis (with over 470 taxi stands to try), car rentals and private tours. However, these are much more expensive than the Métro or bus and not that much more convenient than public transportation.
Paris is a huge city with one of the best and most user-friendly public transportation systems in the world. The only big caveat is that escalators in the Métro are frequently broken, necessitating long walks up large flights of stairs and problems for anyone in a wheelchair or with other mobility issues. That said, there is the bus. Public transportation works equally well otherwise for both Parisians and travelers. You might even call it one of the better parts of a well-rounded Paris experience!