During the last decade there has been increased recognition of the prevalence of antenatal depression as well as an expansion in research examining the impact of maternal mood during pregnancy on offspring development. The aim of this review was to summarise the theoretical underpinnings and empirical evidence regarding the impact of antenatal depression on children's developmental outcomes. Biological mechanisms hypothesised to account for an association between antenatal depression and adverse offspring outcomes are first identified including the functioning of the prenatal Hypothalamic Pituitary Adrenal (HPA) axis and epigenetic processes. A systematic literature search is then conducted of studies examining the impact of antenatal depression on child development. In general, studies examining associations between antenatal depression and offspring temperament, cognitive and emotional outcomes reveal either no effect of the prenatal environment or small effects that often attenuate following adjustment for other antenatal and postnatal risk factors. In contrast, an independent effect of antenatal depression on children's conduct problems and antisocial behaviour is a well-replicated finding. There is emerging evidence that exposure to depression during pregnancy impacts negatively on offspring biology, although the findings are complex and require replication. Psychological and pharmacological treatments of antenatal depression are then reviewed, considering whether antidepressant medication exerts harmful effects on the foetus. We close by proposing that antenatal depression is an early marker of a developmental cascade to future mental health problems for both mothers and offspring.