Orly Airport to central paris
Your travel options summarised...
For the first time visitors:
Go C Paris shuttle bus to Pont de Rungis then RER C to Gare de Austerlitz for 6.35€
OrlyBus to Denfert Rochereau for 9.50€
Les Bus Direct (ex 'Les Cars' Air France) to Montparnasse / Invalides / Champs Elysées for 12€
OrlyVal to Antony, then RER B to Châtelet for 12.10€
Magical shuttle Orly to Disneyland Paris bus for 23€ (10€ kids)
For the more experienced or budget travellers:
Paris city bus #183 to Porte de Choisy for 2€ then another 1.90€ for Metro into central Paris
Tram 7 (not shown on directory) to South East Paris Metro station of Villejuif-Louis Aragon on Paris Metro line 7 for 1.90€ (Tram) + 1.90€ (Metro)
'Le Bus Direct' are very comfortable coaches which are a good option for transfer From Paris Orly into the city.
The benefit of using the coach is that it is direct and your luggage is put on/taken off the coach by the driver.
The RER line B train & OrlyVAL shuttle train option means changing at 'Antony' station and carrying and minding your own luggage.
The Orlybus means carrying your luggage with you on the bus and then taking the RER train/metro from Denfert-Rochereau station.
Taxis are available if money is no problem but for the average traveller one of the options above would be better.This also applies to the shuttle services which allow you to keep the price down by sharing with fellow travellers or privately for a group.