This thesis brings together a series of work undertaken in partial fulfilment of the Doctorate in Clinical Psychology. Volume I – Research: Literature review; empirical paper; and public dissemination document providing an accessible summary of this volume. The literature review draws together the extant literature on what is known about what happens when the police detain people experiencing mental health crises. It offers a systematic search of relevant bibliographic databases, and findings are discussed within the context of the limitations of the review and the implications for future practice and research. In building on the work of this review, the empirical paper goes on to explore how police officers understand and experience the use of Section 136 of the Mental Health Act (1983/2007). This study employed interpretative phenomenological analysis to explore ten officers’ (from the English Midlands) experiences of this aspect of their work. Volume II – Clinical practice reports: Outlining work undertaken on placements from adult, older adult, learning disability, and physical health specialties. The reports consist of: a case study illustrating a dual formulation approach; a service evaluation; a single case experimental design study; a case study; and the abstract for an oral presentation of a case study.