Competition is an integral part of sport. In this chapter, the authors discuss some of the research conducted in the context of sport that is directly relevant to competition. First, the authors briefly introduce the different types of competition and “appropriate” competition. Then, they discuss the effects of sport competition on select athlete outcomes, specifically performance, enjoyment, anxiety, choking, prosocial behavior, and antisocial behavior. In this discussion, the authors consider the mechanisms that explain the effects of competition on performance, with particular attention to team competition, how extreme anxiety can lead to choking, the theoretical explanations of choking under pressure, and how certain sports could facilitate some types of prosocial behavior. Next, the authors discuss challenge and threat states in sport competition and continue with an overview of how certain personality traits and motivational orientations could influence psychological and behavioral outcomes in sport competition. The authors conclude the chapter with a section on how to create an optimal competitive environment in sport.