Parent-child book reading (PCBR) is effective at improving young children's language, literacy, brain, and cognitive development. The psychosocial effects of PCBR interventions are unclear. To systematically review and synthesize the effects of PCBR interventions on psychosocial functioning of children and parents. We searched ERIC, PsycINFO, Medline, Embase, PubMed, Applied Social Sciences Index and Abstracts, Social Services Abstracts, Sociological Abstracts, Family and Society Studies Worldwide, and Social Work Abstracts. We hand searched references of previous literature reviews. Randomized controlled trials. By using a standardized coding scheme, data were extracted regarding sample, intervention, and study characteristics. We included 19 interventions (3264 families). PCBR interventions improved the psychosocial functioning of children and parents compared with controls (standardized mean difference: 0.185; 95% confidence interval: 0.077 to 0.293). The assumption of homogeneity was rejected (Q = 40.010; P < .01). Two moderator variables contributed to between-group variance: method of data collection (observation less than interview; Q = 7.497; P < .01) and rater (reported by others less than self-reported; Q = 21.368; P < .01). There was no significant difference between effects of PCBR interventions on psychosocial outcomes of parents or children (Q = 0.376; P = .540). The ratio of moderating variables to the included studies limited interpretation of the findings. PCBR interventions are positively and significantly beneficial to the psychosocial functioning of both children and parents.