Recent estimates are that close to 30 million children between the ages of 6 and 18 years participate in team sport and close to 60 million in some type of organized athletics in the United States. This has resulted in an increase in sport-related injuries, but the reasons for this are complex and multifactorial. Sport participation offers multiple benefits for children and adolescents, but there is concern that early sport specialization (ESS) may lead to adverse health and social effects. ESS has been defined as intensive training or competition in organized sport by prepubescent children (<12 years of age) for more than 8 months per year, with focus on a single sport to the exclusion of other sport and free play. An increased prevalence of ESS has been attributed to multiple variables, including coach/caregiver influence and the perception that developing athletes can attain mastery and gain a competitive advantage. Trends vary across individual and team sport and by sex. It has been proposed in the literature and lay press that a lack of diversified activity in youth leads to overuse injury, psychological fatigue, and burnout. ESS may not be necessary for elite athletic achievement, and the contrary has been proposed that early sport diversification leads to superior results. This review will summarize the current understanding of ESS, report evidence for and against its merits, highlight areas of future research, and provide recommendations for orthopaedic providers involved in the care of young athletes.