The billionth journey using contactless payment has been made on London's public transport network, Transport for London (TfL) has announced.
Since the technology was introduced to the capital in December 2012 its popularity has soared.
Some 40% of all pay as you go trips are now made using contactless, up from 25% early last year.
Most of the payments are made using credit or debit cards, but many passengers also use mobile apps, key fobs, stickers or wristbands.
Mayor Sadiq Khan said: "I'm delighted that we've hit one billion contactless journeys in London.
"The dramatic increase in the use of contactless over the last year shows the real progress we've made making journeys easier and more convenient for busy Londoners and also visitors to our city."
TfL chief technology officer Shashi Verma said the payments have "completely transformed the way people pay for travel in London".
Last year TfL signed a deal worth £15 million to allow Cubic Transportation Systems to adapt London's contactless ticketing system worldwide.
Mr Khan said: "London continues to lead the way in terms of contactless payment around the world, and the money we make selling TfL's innovation and expertise to other major global cities will allow us to put further money into improving London's own transport network."
Britain's biggest bus operator Stagecoach has rolled out contactless payment in a number of English regions, including Greater Manchester, South Yorkshire, Oxford and the South East.