This review draws attention to the broad and diverse theoretical underpinnings of interpersonal psychotherapy (IPT). A plea is made for greater attention to the theoretical influences on IPT in forming our understanding of the techniques and processes and to establish indicators of successful outcome as well as for whom the treatment is most suitable. The paper takes a lifespan perspective that considers the implications of social factors for the different age groups to which IPT has been shown to be effective in the treatment of depression. The main thrust of the paper considers the potential importance of social theory, particularly the research on life events and social support. It is argued that it is these social aspects and particularly a focus on the use of the patient's wider social network that distinguishes IPT from other evidence‐based short‐term therapies. Copyright © 2012 John Wiley & Sons, Ltd.Key Practitioner Message Interpersonal psychotherapy draws on a broad and diverse range of theoretical influences. The study of the theory underpinning IPT can inform assessment, technique and process in the practice of IPT. Knowledge of aspects of the research on life events and social support is particularly relevant not only for the assessment phase but also for the middle and termination phases. Attention to the theory behind IPT can usefully inform future research on IPT particularly what may determine successful or unsuccessful outcome of this short‐term treatment.