There are two major airports in Paris. Charles de Gaulle and Orly. This quick guide explains how to get to/from the airports by public tranportation.

From ORLY Airport.

You can travel two ways from Orly airport. One is by bus/metro combination or the other is shuttle/RER Train. I have found the most convenient way is by taking the Orlybus. When you exit Orly Airport you will walk to the right and there you will find the green/white Orlybus. The fare is 35F (about $7US). This bus will take you to the Denfert-Rochereau metro/RER train stop. Here you enter the metro system and go wherever you want (read on for metro info). There is also an Air France bus that goes to Gare Montparnasse and the Arc de Triomphe for 40F.

From Charles de Gaulle

CDG airport you can take the Roissy Bus that takes you to the heart of Paris at the Opera metro stop. The fare is 30F ($6US).

These buses run every 15 minutes during anytime of day you could possibly need to get to the airport. If you decide to take a taxi from the Eiffel Tower it will cost between 125F to 250F. Paris taxi's can only accomdate 3 people and very little luggage so you are forewarned.

If the RATP is on strike then the Orlybus will not be running. If Air France is on strike the Air France buses will not be running.