Background: In three academic articles, this PhD thesis investigates maternal postpartum depression (PPD) as a risk factor for the infant-mother attachment and infant development. Previous studies have been contradictory with respect to the question of whether PPD can have long term effects on offspring. This may be due to not differing between when PPD is only occurring in the postpartum period and when effects are also due to ongoing or recurrent depression. However, it may also be due to viewing maternal depression as a unitary construct, and not considering underlying maternal psychological difficulties which may moderate potential adverse effects. The present thesis investigates two potential maternal moderators of risk:. Comorbid personality disorder and adult attachment insecurity. Moreover, the question of early environmental effects of PPD versus effects of later or ongoing depression is addressed. Method: Mothers (N=90) were recruited into a longitudinal study and assessed with Edinburgh Postnatal Depression Scale, and the clinical interviews Present State Examination, Structured Clinical Interview for DSM-IV Axis II, and Adult Attachment Interview. Infants were assessed at four and 13 months with the Bayley Scales of Infant and Toddler Development, third edition. Additionally, at 13 months infant-mother attachment security was assessed using Strange Situation Procedure. Results: We found that even in a well-functioned sample, symptoms of depression in the postpartum period was associated with more symptoms of personality disorder and higher levels of a preoccupied insecure state of mind regarding attachment (PhD paper 1). With regard to infant outcomes, we found that PPD was associated with poorer cognitive development at four months but not at 13 month (PhD paper 2) and that infants of mothers with both personality disorder and PPD were at greater risk of developing an insecure attachment relationship with their mother at 13 months than infants of mothers only suffering from PPD or infants of mothers with no psychopathology. Interestingly, infants of mothers who only had PPD were not more likely to be insecurely attachment than infants of comparison-mothers. Conclusion: Parenting problems may not be an inevitable consequence of PPD. When investigating effects of PPD on offspring, it is important to take into account co-occurring maternal psychological factors that may not only buffer or amplify effects , but which may also increase the risk of recurrent or persistent depression in the mother. These findings are also important in terms of providing appropriate help with the aim of preventing adverse developmental outcomes in the child. For a large group of PPD mothers, depression may not be the only problem to address. In this case, a focus on the mother-infant relationship is vital. Another group of PPD mothers seems to be able to provide sensitive caregiving, despite the depressive symptoms. In this case, a more specific focus on reducing depressive symptoms seems more appropriate.