This systematic review and meta-analysis evaluates the effect sizes of randomized trials of psychotherapies for depression across different age groups. Importance It is not clear whether psychotherapies for depression have comparable effects across the life span. Finding out is important from a clinical and scientific perspective. Objective To compare the effects of psychotherapies for depression between different age groups. Data Sources Four major bibliographic databases (PubMed, PsychINFO, Embase, and Cochrane) were searched for trials comparing psychotherapy with control conditions up to January 2019. Study Selection Randomized trials comparing psychotherapies for depression with control conditions in all age groups were included. Data Extraction and Synthesis Effect sizes (Hedges g) were calculated for all comparisons and pooled with random-effects models. Differences in effects between age groups were examined with mixed-effects subgroup analyses and in meta-regression analyses. Main Outcomes and Measures Depressive symptoms were the primary outcome. Results After removing duplicates, 16756 records were screened and 2608 full-text articles were screened. Of these, 366 trials (36702 patients) with 453 comparisons between a therapy and a control condition were included in the qualitative analysis, including 13 (3.6%) in children (13 years and younger), 24 (6.6%) in adolescents (>= 13 to 18 years), 19 (5.2%) in young adults (>= 18 to 24 years), 242 (66.1%) in middle-aged adults (>= 24 to 55 years), 58 (15.8%) in older adults (>= 55 to 75 years), and 10 (2.7%) in older old adults (75 years and older). The overall effect size of all comparisons across all age groups was g = 0.75 (95% CI, 0.67-0.82), with very high heterogeneity (I-2= 80%; 95% CI: 78-82). Mean effect sizes for depressive symptoms in children (g = 0.35; 95% CI, 0.15-0.55) and adolescents (g = 0.55; 95% CI, 0.34-0.75) were significantly lower than those in middle-aged adults (g = 0.77; 95% CI, 0.67-0.87). The effect sizes in young adults (g = 0.98; 95% CI, 0.79-1.16) were significantly larger than those in middle-aged adults. No significant difference was found between older adults (g = 0.66; 95% CI, 0.51-0.82) and those in older old adults (g = 0.97; 95% CI, 0.42-1.52). The outcomes should be considered with caution because of the suboptimal quality of most of the studies and the high levels of heterogeneity. However, most primary findings proved robust across sensitivity analyses, addressing risk of bias, target populations included, type of therapy, diagnosis of mood disorder, and method of data analysis. Conclusions and Relevance Trials included in this meta-analysis reported effect sizes of psychotherapies that were smaller in children than in adults, probably also smaller in adolescents, that the effects may be somewhat larger in young adults, and without meaningful differences between middle-aged adults, older adults, and older old adults. Question Do psychotherapies for depression have comparable outcomes in age groups across the life span? Findings In a meta-analysis of 366 randomized clinical trials including 36072 patients comparing psychotherapy with control conditions, psychotherapies had lower effect sizes in children and adolescents compared with adults, and no significant differences were found between middle-aged and older adults. However, conclusions are not definitive, given the low quality of many studies, the risk of publication bias, and the high heterogeneity among the studies. Meaning There is a need to improve psychotherapies in children and adolescents.