The most practical as said by Doug Or is the Air France bus that takes you directly from CDG
Alternative means is by RER or the suburban train. You have to take RER B direction St Remy les chevreuse, descend at Antony to take the Orly Val (the automatic train going to terminals in ORY
). There is an RER ticket window and station at CDG2, from CDG
1 it is even less practical since you have to take a shuttle to the station.