Welcome to the new future of involvement. Forming groups is easier than it's ever been: unpaid volunteers can build an encyclopaedia together in their spare time, mistreated customers can join forces to get their revenge on airlines and high street banks, and one man with a laptop can raise an army to help recover a stolen phone. The results of this new world of easy collaboration can be both good (young people defying an oppressive government with a guerrilla ice-cream eating protest) and bad (girls sharing advice for staying dangerously skinny) but it's here and, as Clay Shirky shows, it's affecting! well, everybody. For the first time, we have the tools to make group action truly a reality. And they're going to change our whole world.