Formulation is deemed to be a cornerstone of skilled psychological practice. It has been identified as central to the work of the professional psychologist (British Psychological Society, 2005) and is a pivotal skill of the scientist-practitioner. Yet the use of and process by which formulations are created is contentious. For example, the concept is problematic for many practitioners operating within existential and phenomenological frameworks who see their work with clients as reflecting an unfolding process rather than the imposition of the psychologist’s worldview upon the client. For others (e.g. Lane, 1974, 1978, 1990) the term has always included the client’s construction of the world and a partnership process in which both client and psychologist create a shared model which forms an agreed process for experiments with behaviour.