The Paris area has two international airports: Roissy Charles-de-Gaulle (CDG) and Orly (ORY).
From Orly aiport take the Orly Val direction Antony until Antony. Take there the RER B direction St Rémy-les-Chevreuse until Le Guichet (about 45 min from Orly).
From Roissy Charles de Gaulle airport take the RER B direction St Rémy-lès-Chevreuse until Le Guichet (about 1 hour 15 min).
Once at the stop Le Guichet, either phone +33 1 69 08 55 29 so that we get there and catch you or cross under the railway lines to reach the bus stop beyond the café close to the station. Take the ATPR bus line 269.02 "Le Guichet-Saclay"(taxis are also available) and get off at the stop Orme des Merisiers (about 15 min), almost facing the CEA Orme des Merisiers entrance.