I’ve written about the Roissy bus before, but want to mention it again as it’s such a useful service, and one that we almost always use now when we are in Paris.
The Roissy bus is a great way to get to and from Charles de Gaulle airport in Paris. On our last trip, we arrived at Terminal 2A and just followed the signs to the bus stop, which is just outside one of the entrances. The bus comes about every 15-20 minutes and is clearly marked Roissy to Paris Opera. You can pay the driver or buy a ticket at the machine inside beforehand. It costs 11 euros one way. It’s comfortable, convenient, easy (and safe) once you’re on.
The bus goes around to 2B, 2D etc, and to Terminal 1 and then directly to Opera (that’s the fancy Opera Garnier, close to the big department stores, Galeries Lafayette and Printemps). It will get you into town in 45-60 minutes, depending on traffic. At Opera it drops you off on rue Scribe, which is to the side of the Opera building. From here you can easily connect by Metro to many other places. Metro lines 3, 7, 8 run through here.
Ditto going back to the airport. It drops off at Terminal 2A first, then goes round to the others. The first bus leaves Opera at 5:15am, and from CDG at 6-ish.
Check out at http://www.ratp.fr/en/ratp/r_61872/roissybus/