Transportation

Métro and Bus

	The métro (subway) is cheap, frequent, clean, safe, and convenient to most places in the city. The only problem is the frequent occurrence of begging (and the occasional presence of pickpockets) in the trains. The trains run from about 5 a.m. to 1 a.m. Lines have numbers, but they are usually referred to by the names of their end stations (e.g. "Vincennes - La Défense"), and this is how you find your way inside the system. Station exits are marked with blue Sortie signs, and exchanges with orange Correspondance signs. A wallet-sized map of the métro is useful to plan your trips.
If you are staying for no more than two or three days of any given calendar week, the best deal consists of buying a carnet, which is a set of 10 tickets sold for about the price of six (currently 10 euros, or $12). Each ticket is good for a single trip, including transfers, but has no date limit. Keep the ticket until you complete your trip, as tickets are occasionally checked inside the trains or on the platforms. These tickets are also valid on city buses, but there are no transfers, so to take a trip that combines the subway and two bus lines, you will need three tickets.
	If you use the subway for at least four or five days of the same week, or are moving to Paris for a while, consider getting a carte orange. The first step is the hardest: you must ask for a carte orange application at a ticket window, fill the form and the card attached to it, and take them back with an ID picture. You won't be charged anything for the card itself. You will then be able to buy a weekly, yellow coupon which looks exactly like a single-trip ticket, and is used in the same way, except that it is good for unlimited trips from a Monday morning through the following Sunday night.
Coupons have different prices according to how wide an area around Paris they are good for. Buy one for "zones 1 and 2" if you are only visiting Paris itself; it costs around 15 euros ($18). When you buy the coupon, you must write on it the number which is printed on your carte orange. The plastic holder they give you to put the card in has a slot to hold the coupon. If you take a bus, just wave the whole carte orange (with coupon) to the driver as you board. If you intend to do a métro marathon on any single day, the "Formule 1" ticket, valid for unlimited rides for just one day, may be more advantageous than single tickets.

Taxis

Speaking of the taxi rides from the airports to the city, there is also public transportation available from the airports, but unless you're on a tight budget, it is very inconvenient: you have to take a shuttle to the RER line, and you end up on a regular commuter line that stops ten times before reaching the city. In addition, line B from CDG airport to the city is plagued by pickpockets who make a business of stealing the laptop bags of business travelers...

Car Rental

If you do need a rental car, reserve it from the U.S. before leaving, using some frequent renter plan (Avis Wizard, Hertz #1 Club, etc.) or your company's corporate rate. A last minute rental in France, without unlimited mileage, could cost as much as 200 euros per day without gas if you drive quite a bit. But a pre-reserved car with a good plan can be as little as 55 euros ($66) per day, with unlimited mileage (but still without gas). In all cases, remember than gas costs about $5 per gallon (it is priced in euros per liter, of course).

Trains

The rapidly expanding TGV network (Train à Grande Vitesse, or high-speed train) connects Paris to large countryside cities like Lyons, Marseilles, Le Mans, Nantes, Lille, Bordeaux, etc., at speeds of up to 185 mph. They run very frequently (e.g. about 15 daily trips each way to and from Lyons) and you can eat in the train. This may allow you to take a day trip to another city, while driving there would force you to stay overnight, and flying would be more expensive. Count about $150 per person for a round trip to Lyons (the 270 miles from Paris' appropriately named "Gare de Lyon" station take exactly two hours, so does the 225-mile trip from Paris' Maine-Montparnasse station to Nantes).

The London-Paris Eurostar service, which goes under the "Chunnel," takes two and a half hours, but that's the Brits' fault -- the train has to use normal (slow) tracks on most of the English side. Note that you have to go through a security checkpoint for the Eurostar, so you must arrive at least twenty minutes in advance of the departure, or you will be denied boarding, and you need an ID since you are crossing a border. Business fares on the Eurostar are quite expensive (as much as $380 one-way), but you can get much lower "promotion" rates for leisure roundtrips on the week-end.

Reservations are advisable on all long distance trains and are compulsory on most TGVs. The easiest way (but still an exercise in patience with the French public "service" bureaucracy) is to go to any one of the six major railway stations in Paris (Gare Saint-Lazare, Gare du Nord, Gare de l'Est, Gare de Lyon, Gare d'Austerlitz, Gare du Maine-Montparnasse - there is a subway station at each of them), not necessarily the one from which you will be leaving, to find about schedules, fares, and make a reservation. Note that there are more English-speaking agents at Gare Saint-Lazare and Gare du Nord because this is where trains leave to connect to England-bound ferries (the Eurostar leaves from Gare du Nord). Look for the Réservation Grandes Lignes counters (long distance reservations). The other end of the station, labeled Banlieue (suburbs) is for commuter trains. Tickets and reservations can also be obtained from automatic tellers with touch screens, but they only take French credit cards ("smart" cards with a chip embedded in the card), not foreign cards which only have a magnetic strip.