If you arrive at Charles de Gaulle Airport, Terminal 2A, on American Airlines you have a number of choices as to how to get into the city.
Some people will always catch a taxi (expensive), others swear by the RER B train to the city center—Gare du Nord, Chatelet, or San Michel are all good central stops to then connect to the wonderful Metro system.
However, another option that we’ve come to prefer is to catch the Roissy Bus. Why do we prefer it? Well, it’s a bit cheaper than the RER B train ticket, it’s easier to get your luggage on and off the bus, and it’s safer in that it’s smaller and less crowded than the train so the notorious pick-pockets would have a hard time preying on tired and/or unsuspecting passengers. It’s also easier and quicker to get your ticket as you just buy it from the driver when you board (but you do need cash).
Go to Gate 9 at Arrivals in Terminal 2A and the clearly-marked Roissy Bus to Opera comes about every 15-20 minutes between 5:45am and 11pm. Board at the front, pay the driver 10 euros per person one way, and sit back for 45-60 minutes (depending on traffic). It also stops at Gate D11 for Terminals 2B and 2D, and at Gate 32 for Terminal 1. The bus goes directly to Rue Scribe, at the side of the famous Opera Garnier, and it’s very easy to walk around the corner to the front of the Opera and find the Metro entrance.
Note: If you fly into Orly Airport, the Orly Bus goes to Denfert-Rochereau station, also a good connection point for RER trains and Metro to the city.