This paper sets out to consider a psychodynamic approach to postnatal depression. In particular, it examines the advantages of psychodynamic parent — infant psychotherapy both as a treatment model and also as a way of thinking that can help to formulate a theory of the postnatal period. An illustration is provided in the clinical account of the therapy of a couple and their nine-week-old infant. The author draws on this example, and on findings from psychoanalytic theory, infancy research, evolutionary biology and anthropology to suggest an integrated understanding of the postnatal state of mind and its challenges.