Loads of scouts from 160 countries have gathered in Essex in south east England to celebrate the 100th birthday of their organisation.
The 12-day event was opened by Prince William, who flew in by helicopter. He met lots of young people, who told him about the activities on offer.
The 21st World Scout Jamboree will be packed with lots of adventure activities and fun and games.
Prince William gets involved - nice dancing!
The Scouting Movement was set up in 1907, with the first camp held in Dorset. As you can see, it's still going strong!