Self-regulation develops rapidly during early childhood and is essential for academic and social adjustment. However, previous research has attempted to define the conceptualization and structure of self-regulation differently, leaving the field with an incomplete picture. The nature of the relations between self-regulation and early child outcomes and the factors that affect these relations are not well understood. This meta-analysis synthesized results from 57 studies (109 effect sizes; total n = 15,760, age range = 36–96 months) to investigate the relations between the behavioral, cognitive, and emotional aspects of self-regulation and academic and social competence. We also examined the moderating effects of individual and study characteristics. Results showed that the behavioral and cognitive aspects of self-regulation were associated with math, language, and literacy performance, and all aspects of self-regulation were related to social competence, but with varied magnitude. Moderating effects were identified in several associations in which the self-regulation assessment approach was the most important moderator, with parent-report measures consistently producing smaller effect sizes. Overall, the findings support the multidimensionality of self-regulation and reveal differential relations between its components and child outcomes. The mechanism of these associations and the choice of self-regulation measures and approaches, and implications for research and professional practices, are discussed.