Infant attachment theory is now nearly seventy-years old. Despite debates that developed around the original theory relating to the role of the mother and the potential for emotional flexibility in the infant, its core thesis of the role of the 'Internal Working Model' in human mental health endures. Recent neurophysiological research reveals complex relationships between stress biology and infant attachment. In this article, attachment theory is summarised from its origins to its currently emerging relationship with neurophysiology, and implications for policy are discussed. Emergent concepts include the indication that insecure relationships in infancy have the potential to impact upon lifelong mental health, and that contemporary UK policy does not give enough weight to this finding when planning care and social strategies for infants and their families. This article attempts to bring together a cohesive picture of research across neurophysiology, psychology and practice to inform future policy development.