Objective To assess the effects of psychosocial and psychological interventions compared with usual antepartum, intrapartum, or postpartum care on the risk of postnatal depression. Data sources Medline, Embase, CINAHL, Cochrane central register of controlled trials, Cochrane pregnancy and childbirth group trials register, Cochrane depression, anxiety, and neurosis trials register, secondary references and review articles, and experts in the field. Study selection All published and unpublished randomised controlled trials of preventive psychosocial or psychological interventions in which the primary or secondary aim was a reduction in the risk of postnatal depression. All trials recruited pregnant women or new mothers less than six weeks postpartum. Eligible studies were abstracted, assessed for methodological quality, and pooled with relative risk for categorical data and weighted mean difference for continuous data. Results Fifteen trials with 7697 women were included. Although there was no overall statistically significant effect on the prevention of postnatal depression in the meta-analysis of all types of interventions (15 trials, n = 7697; relative risk 0.81, 95% confidence interval 0.65 to 1.02), these results suggest a potential reduction in postnatal depression. The only intervention to have a clear preventive effect was intensive postpartum support provided by a health professional (0.68, 0.55 to 0.84). Identifying women “at risk” assisted in the prevention of postnatal depression (0.67, 0.51 to 0.89). Interventions with only a postnatal component were more beneficial (0.76, 0.58 to 0.98) than interventions that incorporated an antenatal component. In addition, individually based interventions were more effective (0.76, 0.59 to 1.00) than group based interventions (1.03, 0.65 to 1.63). Conclusions Diverse psychosocial or psychological interventions do not significantly reduce the number of women who develop postnatal depression. The most promising intervention is the provision of intensive, professionally based postpartum support.