The present meta-analysis integrates the effects of randomized controlled trials that focus on promoting effective parenting in the transition to parenthood. We included 142 papers on interventions which started during pregnancy or in the first 6 months after birth. Computations were based on random-effects models. On average, interventions had small to very small significant effects on parenting (d = .35 SD units), parental stress (d = .20), child abuse (d = .13), health-promoting behavior of parents (d=.15), cognitive development (d = .24), social development (d = .30), motor development of the child (d = .15), child mental health (d = .40), parental mental health (d = .31), and couple adjustment (d = .13). Most of the effects were maintained at follow-up. Effects varied by onset of the intervention, delivery mode, qualification of the intervener, length of intervention, intervention goals, and gender distribution. In addition, we found that older studies reported greater effect sizes. We conclude that parenting-focused interventions are effective and should be made accessible to more expectant and new parents.