The most charming of Paris' public transport options the underground Métropolitain (and its sister system the RER) is a simply massive network. No matter where you are chances are there's a metro station within a few blocks. Likewise the public bus system runs everywhere but its hours are laughable and don't even try to hop aboard on Sunday or a holiday. The Noctambus network takes over in the heavily trafficked areas once both the underground and the day buses go to sleep.

In case you hadn't guessed it driving around Paris is a job best reserved for the terminally aggressive - if you don't have lots of time to kill you're better off taking public transport. Likewise with bicycles: Parisians don't much like to share the road and bikes aren't allowed on the metro.

Best way within the city (NOT including the CDG or Orly airports) is to get a carnet of 10 metro tickets and use to come and go as you please. Obviously if you don't use some of the tickets they're not refundable. So if you won't use 10 tickets, just get individual tickets.

AIRPORT to CITY: RER (regional express train) - it's cheap, quick, and very comfortable.

NEVER a bus - it takes ages if it even arrives. Sometimes it will arrive but won't stop, so you'll just have wasted loads of time (bec buses are perpetually late).

There's ticket machines in the both terminals of CDG (section D in terminal 2). They operate only with coins (euros) or credit cards.