This meta-analytic review examines gender differences in emotion expression from infancy through adolescence, focusing on facial, vocal, and behavioral expressions. The study analyzed 555 effect sizes from 166 studies involving 21,709 participants. Key findings include: 1. **Overall Gender Differences**: Girls showed more positive emotions (g = -0.08) and internalizing emotions (e.g., sadness, anxiety, sympathy; g = -0.10) than boys, while boys showed more externalizing emotions (e.g., anger; g = 0.09) than girls. 2. **Age Moderation**: Gender differences in positive emotions were more pronounced with increasing age, with girls showing more positive emotions than boys in middle childhood (g = -0.20) and adolescence (g = -0.28). Boys showed more externalizing emotions than girls at toddler/preschool age (g = 0.17) and middle childhood (g = 0.13), but fewer externalizing emotions than girls in adolescence (g = -0.27). 3. **Contextual Moderation**: Gender differences were less pronounced with parents and more pronounced with unfamiliar adults (for positive emotions) and with peers/when alone (for externalizing emotions). 4. **Theoretical Frameworks**: The study draws from biological, social developmental, and social constructionist theories to explain gender differences in emotion expression. Biological theories highlight innate differences, social developmental theories focus on learning and socialization, and social constructionist theories emphasize the role of context. 5. **Methodology**: The review included studies from 1979 to 2010, using a comprehensive literature search and coding system to ensure data quality. 6. **Hypotheses and Results**: The study tested hypotheses about gender differences in positive, internalizing, and externalizing emotions, as well as general negative emotions. Results showed significant but very small gender differences in all emotion categories, with girls showing more positive and internalizing emotions and boys showing more externalizing emotions. The findings have important implications for understanding gender differences in children’s healthy and maladaptive development, emphasizing the importance of contextual factors in these differences.This meta-analytic review examines gender differences in emotion expression from infancy through adolescence, focusing on facial, vocal, and behavioral expressions. The study analyzed 555 effect sizes from 166 studies involving 21,709 participants. Key findings include: 1. **Overall Gender Differences**: Girls showed more positive emotions (g = -0.08) and internalizing emotions (e.g., sadness, anxiety, sympathy; g = -0.10) than boys, while boys showed more externalizing emotions (e.g., anger; g = 0.09) than girls. 2. **Age Moderation**: Gender differences in positive emotions were more pronounced with increasing age, with girls showing more positive emotions than boys in middle childhood (g = -0.20) and adolescence (g = -0.28). Boys showed more externalizing emotions than girls at toddler/preschool age (g = 0.17) and middle childhood (g = 0.13), but fewer externalizing emotions than girls in adolescence (g = -0.27). 3. **Contextual Moderation**: Gender differences were less pronounced with parents and more pronounced with unfamiliar adults (for positive emotions) and with peers/when alone (for externalizing emotions). 4. **Theoretical Frameworks**: The study draws from biological, social developmental, and social constructionist theories to explain gender differences in emotion expression. Biological theories highlight innate differences, social developmental theories focus on learning and socialization, and social constructionist theories emphasize the role of context. 5. **Methodology**: The review included studies from 1979 to 2010, using a comprehensive literature search and coding system to ensure data quality. 6. **Hypotheses and Results**: The study tested hypotheses about gender differences in positive, internalizing, and externalizing emotions, as well as general negative emotions. Results showed significant but very small gender differences in all emotion categories, with girls showing more positive and internalizing emotions and boys showing more externalizing emotions. The findings have important implications for understanding gender differences in children’s healthy and maladaptive development, emphasizing the importance of contextual factors in these differences.