Ile-de-France: Tickets and Passes
A ticket worth €1.90 is valid for all the subway, bus, tram (without transfers), RER and SNCF (zones 1-2), the Montmartre funicular. A 10-ticket book for Carnet costs €14.90. The lilac ticket is valid for 2 hours till exiting subway turnstiles. It's available at subway offices or tobacco/news stands.
New Tickets t+
They allow transferring within 1 transport means on various buses, trams and the subway with 1 ticket for 1.5 hours. For transfers like subway-bus you'll have to buy another ticket.
Bus tickets marked with sans correspondance are not for transfers. Never throw away subway tickets before exit - they open passage via RER lobbies and choppers occasionally appear in subway cars and corridors.
Transport is free for kids under 4 and costs a half for kids 4-11 old.