Paris-Sud University can be reached either by car or by RER (suburb train network). RER B connects Orsay with both airports (Charles de Gaulle or Orly), and with all parisian train stations, via the subway. You can find a RER map here and a RER schedule here. In RER stations, you will find two types of displays: some give only the final destination of trains (take only "Orsay" or "Saint Remy les Chevreuses") with their passage time. Some give a list of all the stations: the small light in front is "on" if the train stops in the station. Prices indicated below were those of June 2012, they may have been slightly modified by now. A ticket from Paris to Bures-sur-Yvette costs 4.65 euros (a set of 10 tickets costs 37.20 euros). To come to the symposium, you should rather get off at the station "Bures sur Yvette" (RER direction "saint remy les chevreuses") , though it is also possible to walk from "Orsay Ville" (RER direction "saint remy les chevreuses" or "orsay"). From airport Charles de Gaulle We advise you to take RER B (the ticket from CdG to Orsay costs 13.25 euros). Take any train from CdG to Paris (but if possible, it is better to take a direct or semi-direct train, they are much much faster). Then you may have to change in Paris: get off for example in "Luxembourg", stay on the same side and wait for a train that goes to "Bures sur Yvette" (direction "saint remy les chevreuses"), or to "Le Guichet" (direction "Orsay") if you want to reach "Hotel d'Orsay". The taxi from CdG to Orsay costs approximately 100 to 120 euros (in the evening). From airport Orly You have to change in "Antony" (OrlyVal to RER B) From Paris station "Gare du Nord" Direct connection via RER B