Gary and Ron are practicing soccer moves on the playground. They have all their equipment -goal, shinpads, and regulation ball -and they ' re having fun together. Ron shows Gary how to head the ball into the goal, both shouting, " Hurray! " But then things get complicated, changing fast, as interaction often does. Ron, thinking twice about sharing his best technique, kicks the ball away from Gary on the next play. Then Huynh, who had been watching from the sidelines, asks Gary if he can join them. Simultaneously, Gary trips over a swiftly kicked ball and slumps to the ground. And just then, Jack, the class bully, approaches, laughing at Gary ' s discomfort, then angrily demanding they leave so that he and his buddies can use the fi eld. Somehow, Gary deals with all of this. He hands the ball to Huynh, extends a hand to Ron, and calmly tells Jack, " It ' s our turn now. "What do emotions have to do with social development? Our example abounds with instances where emotions help determine the fl ow and outcome of interaction. First, behaviors of others in one ' s social group often constitute antecedent conditions for children ' s emotions. When Ron became angry, it was because his goal of being the " best " was threatened. Huynh approached diffi dently because he often had been " left out " from play. Second, when children exhibit emotion within dyads or groups, this emotional expressiveness also is important information for others involved. When Gary experienced delight at making a goal, he wanted to keep playing; others, like Huynh, wanted to join him. Jack is irritable and easily provoked by those he perceives to be " in his way. " His