disneyland® Paris from Orly by RER 'b' train
To use the RER train system to get you to Disneyland® Paris via its line 3 route you first have to use the Orlyval shuttle train service from the airport to the RER station 'Antony' then take the RER B direction Charles de Gaulle airport to Châtelet les Halles, then take the RER A direction Marne La Vallée Chessy which is the Disneyland® station.
It will cost around €20 in total and will take around 90 minutes. If you are travelling light and on a budget this may work for you but by paying €3.00 more you can take the 'Magical Shuttle' coach and save yourself a fair bit of hassle. If you choose this route, for whatever reason, this will help - Orly to Pairs by train
You need to take the line to Chatelet-Les Halles where you can catch the RER line A4 to Marne-la-Vallee (Disneyland® Paris) - sometimes abbreviated to to 'MLV Chessy' on some display screens.
Chatelet Les-Halles is actually the largest underground station in Europe but don't let that put you off as it is well signposted and provides the largest choice of metro options within the city. You have to make your way to the RER line A4 and take the train in the direction of Marne-la-Vallee. On the Platform you will find an overhead illuminated sign highlighting the route of the arriving train with all the stops on that route lit up.
*Please note: because of the number of lines through this station it is best avoided at peak times.
You will arrive at the station 'Marne-la-Vallee / Chessy, Paris Disneyland®' which is on the plaza between the Disneyland® Hotel, the Walt Disney Studios and the Disney® Village.