You can catch public transportation from each of London's five airports, but your mass-transit journey can even begin before your flight lands with an online purchase of an Oyster card or one of the city's Travel Cards -- electronic smart cards that allow you to pass through turnstiles and gates by waving the card over a sensor. They can be delivered to your home before you leave for your trip, and are offered at a wide range of price levels and discounts. The cards can be used to travel on London's vast mass transit system that includes buses, subways, trams, trains and boats [source: London Mass Transit].
The Tube, London's subway, is the fastest and most efficient way to travel around the city, and offers connections to the Eurostar to Paris as well as trains to other destinations [source: Rail Europe]. You can also take the Docklands Light Railway or DLR, which offers views of the River Thames. If you prefer buses to get a scenic (albeit slower) tour, you can take advantage of London's famous fleet of double-decker buses. The city also has River Bus service that stops at 10 city piers.