There are many features of youth sport that can make it exciting and motivating or, alternatively, make it dull, stressful, or otherwise uninviting. Among those features are the participants themselves. When young athletes sign up for a sport, opt to stay with a particular team, invest time and energy into practicing, or consider their competitive successes and failures, their peers (those of similar age, standing, and power) often play a part. Teammates are probably the most important peers in shaping youth sport choices and experiences, but other peers at school and elsewhere can also influence young athletes. In this article, we describe three ways that peers matter in youth sport. We argue that the quality of young athletes’ sport experiences is tied to specific friendships, broader acceptance by peers, and how athletes compare themselves to their peers. These aspects of peer relationships play important roles in shaping athlete motivation and performance.