Lord Coe has marked two years to the start of the London Olympics by asking fans to consider what they want to get out of the Games.
"There are two years to go until the Games begin and we want everyone to start planning their once in a lifetime experience in 2012," he said.
"Whether it's buying a ticket, becoming a volunteer, being part of our education or culture programmes - there are hundreds of ways you can get involved. Don't wait - to ensure you don't miss out, start planning your Games now." Coe added.
To mark the countdown, four-time Olympic gold medallist Sir Chris Hoy became the first to cycle in the 2012 velodrome.
London mayor Boris Johnson joined Hoy in cycling around the track and marked the two-year milestone by launching an appeal for 70,000 people to volunteer at the Games.
Former Olympic champion Coe said the volunteers would make the difference between "a good and a great Games".