Attachment is a critical feature of early human development. It refers to the close bond a child has to his/her parent that serves the purpose of providing feelings of comfort and security. A considerable amount is now known about the development of attachment, the causes of variation in attachment behaviour and their links with psychological health and disorder. A range of treatments are also available for promoting the security of child-parent attachment in the early years. This chapter provides an overview of attachment theory and research and their implications for clinical practice.