There are a number of ways to get from Charles De Gaulle Airport to the main IETF Hotels (Hotel Concorde La Fayette and Le Meridian Etoile).
Taxi - (cost is approximately €45-50 one way, and the trip is approximately 40 minutes):
There are taxi ranks at Terminal 1, Exit 20; Terminals 2A and 2C, Exit 6; Terminals 2B and 2D, Exit 7; and Terminals 2E and 2F, Exit 1. Standard metered rates into central Paris are around €50. Fares increase by about 15 percent at night, and on Sundays and public vacations
When you're in the taxi line, you can ask the dispatcher (who typically will speak English) for a taxi that accepts credit cards. They will check with the driver for you, since not all taxis take cards. Those that do accept cards have in the past accepted Visa cards, but not American Express.
Air France Les Cars Bus (cost is approximately €13.50 one way, and the trip is approximately 45 minutes):
The Air France Les Cars bus to Hotel Concorde La Fayette and Le Meridian Etoile is “Line 2” (Charles De Gualle to Etoile) and the stop is “Porte Maillot” in front of the Hotel Concorde La Fayette. Find the bus stop at Terminal 1 Arrivals Level exit 34: (according to the Les Cars bus site Terminal 2 2A-2C pickup location at door C2 is under construction and not available - use the Terminal 2 2B-2D pickup location); Terminal 2 2B-2D exit B1; Terminal 2 2E-2F Concourse Level exit 3.
RER Train/Metro (cost is approximately €9.25, and the trip is approximately an hour):
Paris Charles de Gaulle is linked to the city by the metro, which is a quick and easy way to get into Paris. Information for the RER station for the airport is here. You can buy tickets from machines in the station and board the train. More train information can be found here.
The RER/Metro is RER-B (direction to GARE D'ORSAY VILLE) to CHATELET LES HALLES, Paris.
CHATELET LES HALLES, Paris RER-A (direction to GARE du Vésinet Le Pecq) to CHARLES DE GAULLE ETOILE, Paris (L'Arc d'Triomphe).
Change to the METRO at CHARLES DE GAULLE ETOILE, Paris (L'Arc d'Triomphe)
CHARLES DE GAULLE ETOILE, Paris (L'Arc d'Triomphe) METRO line 1 (direction to La Défense / Grande Arche) to Porte Maillot, Paris.
Exit the METRO in front of Le Palais des Congres de Paris.
Alternatively, you can forego the final metro leg and walk a kilometer from the Arc d'Triomphe RER station to the Palais des Congres.