Air France Bus: You don't need to have flown or be flying Air France to take their shuttle service to and from the city. When arriving in Paris you can buy a ticket from the Air France Coaches ticket counter or just follow the signs in the airport to the bus stop and then purchase a ticket at the stand or from the bus driver.
Terminal 1: Gate 34 at the Arrivals level
Terminal B: Gate 6
Terminal D: Gate 6
Terminals E and F: Concourse level Gate 3
Line One (journey time around 45 mins) goes from the airport to Porte Maillot (La Défense) and Charles de Gaulle Étoile (Arc de Triomphe) from 5:45 am to 11 pm. It leaves every 15 minutes and costs €12, which you can pay on board. Passengers arriving in Terminal 1 need to take Gate 34; Terminal 2A and 2C, Gate 5; Terminal 2B and 2D, Gate 6, Terminal 2E and 2F, Gate 3.
Line Four (journey time around 50 mins) goes to the Gare de Lyon and Montparnasse from 7 am to 9 pm. Buses run every 30 minutes and cost €12. Passengers arriving in Terminal 1 need to look for exit 34; Terminal 2A and 2C need to take either Gate C2; Terminal 2B and 2D, Gate B1; and Terminal 2E and 2F, Gate 3.
These also run to the airport. For more information, contact Air France Bus (tel: 01-41-56-89-00 recorded information in English, http://www.cars-airfrance.com).
Roissybus: operated by the Paris Transit Authority (RATP), this leaves from all three terminals (including Terminal 3) every 15 minutes:
Terminal 1: exit 1 on the "Arrivals" level
Terminal 2A & 2C: exit 9 in Terminal 2A
Terminal 2B & 2D: exit 11 in Terminal 2D
Terminal 2E & 2F: exit 5 of the walkway
Terminal 3: "Arrivals" hall exit
In Paris it stops at and leaves from the Air France agency alongside the American Express office on Rue Scribe near Place de l'Opéra.
Service is from 6am to 11pm (every 20 minutes after 7pm) from the airport and 5:45 am to 11 pm (every 20 minutes after 8pm) to it; the cost is €8.40. NB: the bus does not stop automatically, you have to wave it down, so don't miss it! The average journey time is 60 minutes but rush-hour traffic can slow that down considerably.
Air France operates a transfer service between airport Charles de Gaulle and Orly airport. The bus departs from Terminal 1 and Terminal 2 (the same points as the Air France bus to Paris) and it runs every 30 minutes from 6AM to 10:30PM. The price is €16 one-way and the journey time around 50 minutes.