Roissybus is an express bus service run by the RATP (the same company that runs the metro and the RER) that links the Charles de Gaulle airport to the center of Paris (the Opera area). The buses leave every 15-20 minutes from terminals 1, 2 and 3 of Charles de Gaulle airport and the service is available from 6 am to 11 pm every day. The trip takes 45 to 60 minutes depending on the traffic and a ticket costs 8.40 euros.

Tel: 01 49 25 61 87
http://www.ratp.info/orienter/aeroport_roissybus.php