Editor’s note: "An extraordinary number of species—from squid to lizards to humans—engage in play. But why? In this article, adapted from Dr. Sam Wang and Dr. Sandra Aamodt’s book Welcome to Your Child’s Brain: How the Mind Grows from Conception to College (Bloomsbury USA, 2011; OneWorld Publications, 2011), the authors explore how play enhances brain development in children. As Wang and Aamodt describe, play activates the brain’s reward circuitry but not negative stress responses, which can facilitate attention and action. Through play, children practice social interaction and build skills and interests to draw upon in the years to come."