Paris Orly Airport

The fastest option, but also the most expensive, is taking the Orlyval from either terminal 1 or 4 to Antony station (between 06:00 and 23:00, every 5 to 8 minutes, an 8-minute trip), and from there connect to RER B trains to Paris (every 15 minutes max, any northbound train will stop at every station in Paris, the journey to Denfert-Rocherau takes about 15 minutes, to Chatelet les Halles about 23 minutes). Orlyval costs €9.30, and a ticket from Orly airport all the way to Paris costs €12.10 (this ticket allows you to transfer to other RER or metro lines once in Paris). Navigo, Mobilis, or Ticket jeunes, are not accepted on Orlyval (they are although accepted on RER B, as long as they cover at least zones 1-3). Paris Visite is valid on Orlyval.

Another option is to take bus 183 from terminal 4 to Pont de Rungis RER station (between 5:00 and 1:30, every 15 minutes, a 10-minute trip), and from there take a RER C train to Paris (every 15 minutes, 20 min to Bibliothèque François Mitterrand, 28 min to Saint-Michel-Notre-Dame). You may need to buy the tickets at the airport, before taking the bus: the bus only sells SMS tickets which can only be bought with a French mobile phone number, at the RER station you'll be able to buy €4.35 tickets to Paris. Navigo, Mobilis, Ticket jeunes, Paris Visite are accepted as long as they cover at least zones 1–4.

Tramway line T7 has a station under the terminal 4, and goes to Villejuif-Louis Aragon on metro line 7 (between 05:30 (06:30 on Sunday) and 00:30, every 6 to 15 minutes, the trip takes about 30 min to the metro, then another 20 minutes to Chatelet in the center of Paris). You can buy a €1.90 "ticket t+" on the machines at the tram station, that you'll need to validate once you get in the tram. You can not buy your ticket on board. You will need another ticket t+ for the metro. Navigo, Mobilis, Ticket jeunes, Paris Visite are accepted as long as they cover at least zones 1–4. The airport station is not the last one on the line and you want to get on the tram that is on the track closest to the exit from the airport and heading away from the tunnel to the left of the platform.

The Orlybus service (every 10-15 min, between 06:00 and 00:30, €8) connects terminal 4 to Denfert-Rochereau in Paris (RER B, metro 4 and 6), but it's subject to traffic jams and rush hour, so it averages 30 min but can last much longer if the traffic is bad (usually in late afternoon Monday-Friday and Sunday). Mobilis and Ticket jeune tickets are not accepted on this line, but Paris Visite zone 1-5 is accepted. If you buy a single ticket, you will need to buy another ticket in Paris to transfer with the bus, metro or RER.

If you're looking for cheap alternatives, you have two options:

• Monday-Friday, from 06:00 to 20:00: take tram T7 from terminal 4 to Porte de Rungis (15 minutes), then bus 216 (it's a circle line, so you cannot take it in the wrong direction, you will reach Denfert-Rochereau after 30 minutes). You'll just need a ticket t+ (€1.90) that you will validate on both the tram and the bus. You can transfer to other bus or trams in Paris, but will need another ticket to transfer to metro or RER.
• Every day, between 06:00 and 00:20: take bus 183 to Robert Peary, then tram T9 to Porte de Choisy. You'll just need a ticket t+ (€1.90 if bought on a machine at the airport), but the trip takes about 1 hour.

The fastest option, but also the most expensive, is taking the RER B from Paris to Antony (look for trains terminating at either St Rémy lès Chevreuse, Orsay-Ville or Massy-Palaiseau, the journey from Denfert-Rocherau to Antony takes about 15 minutes, from Chatelet les Halles about 23 minutes), and from there take the Orlyval to either terminal 1 or 4 (runs from 05:40 to 23:00, a 8 minutes trip). Orlyval itself costs €9.30, and a ticket from Orly airport all the way to Paris costs €12.05 (this ticket allows you to transfer to other RER or metro lines once in Paris). Navigo, Mobilis, or Ticket jeunes, are not accepted on Orlyval (they are although accepted on RER B, as long as they cover at least zones 1-3). Paris Visite is valid on Orlyval.

Another option is to take the RER C from Paris to Pont de Rungis-Aéroport d'Orly (look for trains terminating at Pont de Rungis, called ROMI, or Massy Palaiseau, called MONA. Do not get off at Orly Ville station, just before Pont de Rungis) (20 min from Bibliothèque François Mitterrand to Pont de Rungis, 28 min from Saint-Michel-Notre-Dame), and from there bus 183 to terminal 4 (between 04:45 and 1:10, every 15 minutes, it takes about 10 min). The trip from Paris costs €4.45 + €1.90 for the bus (you cannot buy your ticket on board of the bus, but you can buy it at Pont de Rungis station), and allows to transfer to other RER or metro lines in Paris. Navigo, Mobilis, Ticket jeunes, Paris Visite are accepted as long as they cover at least zones 1–4.

Take metro line 7 to Villejuif-Louis Aragon (first metro passes at Chatelet at 05:51, the trip from Chatelet takes about 20 minutes, in the center of Paris), and from there tramway line T7 to terminal 4 (the last tram leaves at 00:30, the trip takes about 30 min). You can buy a €1.90 "ticket t+" on the machines at the tram station, that you'll need to validate once you get in the tram. You can not buy your ticket on board, or use the ticket you used for the metro. Navigo, Mobilis, Ticket jeunes, Paris Visite are accepted as long as they cover at least zones 1–4.

The Orlybus service (between 05:35 and 00:00, every 10-15 minutes, €8) connects Denfert-Rochereau in Paris (RER B, metro 4 and 6) to terminals 1-2-3 and 4, but it's subject to traffic jams and rush hour, so it averages 30 min but can lasts much longer if the traffic is bad (usually in late afternoon Monday-Friday and Sunday). Mobilis and Ticket jeune tickets are not accepted on this line, but Paris Visite zone 1-5 is accepted.

If you're looking for cheap alternatives, you have two options:

• Monday-Friday, from 06:00 to 20:00: take bus 216 from Denfert-Rochereau or Stade Charléty (tram T3a) to Saarinen (15 min), then take tram T7 heading to Porte de l'Essonne to Orly Airport (terminal 4) (15 min), You'll just need a ticket t+ (€1.90) that you will validate on both the bus and the tram. You can transfer to other bus or trams in Paris, but will need another ticket if you transfer from the metro or RER.
• Every day, between 06:00 and 00:20: take tram T9 from Porte de Choisy to Four - Peary, then bus 183 to Aéroport d'Orly. You'll just need a ticket t+ (€1.90 if bought on a machine in the tram station), but the trip takes 1 hour.

Noctilien buses serve Orly airport roughly every hour between 01:00 and 05:00:

• Line N131 serves Gare de Lyon, Gare d'Austerlitz, Quai de la Gare, Bibliothèque François Mitterrand, Orly 1-2-3, and Orly 4
• Line N144 serves Gare de l'Est, Chatelet, Bastille, Gare de Lyon, Place d'Italie, and Orly 4

You will need either 2 t+ tickets (€4 if bought on board, €3.80 if bought at a machine), or a Navigo, Mobilis, Ticket jeune, or Paris Visite, covering at least zones 1–4.