The winning design will become part of London Transport Museum's collection and will be reproduced as a poster for display on TfL's transport network.
Entrants are encouraged to use all variety of media and current technologies to create their take on contemporary poster design to reflect London's position as a leading design capital City. The poster must work within the contemporary display contexts of TfL's busy public environments and should conform to the rules and conventions of public display. It is important to remember any piece of advertising design will only have 3 seconds to attract the attention of a passer by."
Full details and a list of prizes are on TfL's site. I've heard that the competition organisers are particularly interested in receiving designs that feature modern life in the following London boroughs: Barking & Dagenham, Barnet, Brent, Camden, Ealing, Hackney, Hammersmith & Fulham, Harringay, Harrow, Islington, Newham, Redbridge, Richmond, Tower Hamlets, Waltham Forest and Wandsworth. Maybe these areas are under-represented in the Tube's current posters!