Here is information about Paris transit passes. (Please note that fares change, so check the RATP website directly for latest information and fares.) Tickets and passes are available in métro and bus stations, as well as RER and train stations, and kiosks at Orly and Charles de Gaulle Airport. You’ll also find a link at the end for a listing of other places in Paris to buy transit tickets and passes.
Please note that many of the métro stations have changed and the people in the ticket booth no longer sell tickets. The major stations, however, are still manned by cashiers. Most of the transactions are now done by bilingual machines which don’t take American credit cards, although the machines they do take cash and coins in euros. I recommend bringing exact change in coins when you go.
Also prices are subject to change and for the most up-to-date information, follow the links provided to check on prices directly at the website(s).
Paris passes are generally good for zones 1 and 2, which are sufficient for most visitors. Tickets to the airports or to Versailles (which are other zones) are best purchased separately since you will likely only be making that trip once or twice, which isn’t enough to justify the higher-priced pass
In my opinion, if your arrival dates jibe with the ones for the Navigo Découverte, that’s the best pass as it allows unlimited travel so you don’t have to fumble and worry with tickets and transfers.