Background: Historically, clinical case studies have played a central role in counselling and psychotherapy training and practice, by allowing practitioners to learn about ideas and interventions being developed by colleagues. In recent years, the development of methods for systematic collection and analysis of case data has made it possible for case study research to begin to make a contribution to the evidence base for therapy policy and practice. Aim: This paper provides an overview of the characteristics of rigorous case study research, introduces a set of studies that exemplify these principles, and reviews the relevance of systematic case study inquiry for policy, practice and training. Conclusions: If case study research is to fulfil its potential as a source of research-based knowledge, it is essential for practitioners to publish more systematic case studies that document the range and scope of everyday therapeutic practice. It is also necessary to carry out further research into a variety of methodological issues associated with single-case inquiry, as a means of further developing this approach to practice-based research.