The unveiling of the slogan comes as today (18 April) marks the beginning of the 100-day countdown to the start of the London 2012 Olympics.
Events are being held up and down the UK to mark the occasion.
These have included the unveiling of a giant set of Olympic rings, which has been made up of 25,000 flowers, at London's Kew Gardens.
The slogan was officially unveiled by Seb Coe, chairman of the London Organising Committee of the Olympic and Paralympic Games (Locog) and chief executive Paul Deighton.
London organisers also revealed that the Red Arrows will perform a flypast across the UK to mark the opening ceremony on July 27.
The RAF aerobatics team will fly over London 2012 sites in Belfast, Cardiff, Edinburgh and London.
Previous Olympic slogans include Sydney's "Share the spirit" in 2000, and Beijing's "One world, one dream" in 2008.
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