Book excerpt: How does a bird flock keep its movements so graceful and synchronized? Most people assume that the bird in front leads and the others follow. In fact, bird flocks don't have leaders: they are organized without an organizer, coordinated without a coordinator. And a surprising number of other systems, from termite colonies to traffic jams to economic systems, work the same decentralized way. Turtles, Termites, and Traffic Jams describes innovative new computational tools that can qhelp people (even young children) explore the workings of such systems—and help them move beyond the centralized mindset.