The concept of the scientist-practitioner started as a way to delineate the profession of psychology as a clinical practice. Based in rationality it marked the desire of the fledging group of those who used psychology in clinical settings to be seen as a distinct profession rather than as a technical adjunct to psychiatry. It also provided a rationale for the methods we used. As noted in Chapter 1, the emergence of this fledgling group differed in the USA, where treatment represented an area of practice, from the UK where it was experimentally led in pursuit of rational diagnosis. The concept provided a justification for our place in clinical work and our differentiation from others who were not psychologists.