(Note: this section is meant more for parents and returning RMs acting as tourists. Missionaries will receive instruction on how they'll be getting around once they are in the field, although most Paris-area missionaries do use a Carte Orange.)
Although you can get around Paris using a rental car, because of traffic and parking problems, you might want to consider the subway system, Métro. The Métro is safe and relatively clean. It runs frequently and everywhere. If you do choose to go by Métro, stop at the information desk in the train station and ask them to help you find a place to purchase a Mobilis, which is a day pass for the Métro and normal buses (Paribus is not included), or a Carte Orange if you're staying longer and need to get out further.
You'll have to specify the number of zones. If you don't plan on leaving Paris, just get zones 1-2. That'll cover everything within Paris's boundaries and it only costs 5.40€. Zones 1-3 includes everything out to Saint Denis and costs a little more at 7.15€ though it may be worth it if you get lost in the Métro.)
And here's a quick tip if you do get lost in Métro: do not leave the gates. Leaving the gates means that you'll have to punch another ticket to get back to your original destination. Just find the right track to go in the right direction and stay in the system.
The Mobilis consists of two tickets: a large id card-sized ticket on which you write your name, and a smaller ticket which you put in the ticket slot to open the Métro gate (the gate gives you back your ticket). You must copy the number of the large ticket onto the small one and put the date you're using the ticket on too. DON'T validate the little ticket on the buses (it'll ruin the ticket) just show the ticket to the driver. And don't even worry about doing that if you get on in the back of the bus, Paris has contrôleurs who do random checks of the buses to make sure that everyone has a valid ticket.
The Carte Orange also consists of two tickets: an ID card for which you must have a photo and a smaller ticket, both of which go into a grey sleeve. The little ticket functions as described above.
You may be tempted to get a Paris Visite ticket, marketed aggressively to tourists. The cheapest one for one day costs 8.35€. Although the attractions have gotten better since I first reviewed this in 1996, the discounts are not that great. Most of them are "companion discounts": buy one, get one free. If you aren't planning
on visiting the places that are listed below or you don't have a companion, the ticket still isn't worth it.
The Paris Museum Pass, in contrast, is 30€ for two days (45€ for 4 days, 60€ for 6 days), and it gives you free entry without waiting to more than 60 Paris museums and monuments including the Louvre. This is worth it if you plan to see four or more sights on the list. For example, the Louvre costs 8.50€ (6€ after 3:00 pm), the Eiffel Tower costs 11.00€, and the Arc de Triomphe costs 8€. One more museum and the ticket is covered. Despite the new rates, it's still one of the best bargains in Paris.