This thesis is submitted in part fulfilment of the requirements for the degree of Doctor of Clinical Psychology (Clin. Psy. D. ) at the University of Birmingham. It includes a research project and clinical work undertaken during the course of clinical training. Volume I of the thesis consists of the research component in the form of two papers. Both papers are written as if for submission to specific journals, although tables and figures have been integrated into the text to aid description. The first paper in Volume I is a review of the stress and attribution literature related to the responses of care staff to challenging behaviour in people with intellectual disabilities. This paper was prepared for the Journal of Applied Research in Intellectual Disabilities. The second paper investigates the impact of stress on attributions of challenging behaviour in care staff in services for people with intellectual disabilities. This paper was prepared for Research in Developmental Disabilities. Included in the appendices to Volume I is a public domain briefing summarising the above research. Other details pertinent to the research are also included in the appendices, including ethical approval documentation. Volume II contains five clinical practice reports undertaken in the specialities of child, adult, learning disabilities, older adult and child and family primary care. The reports include a case study of a 13 year old boy who presented with `panic attacks', formulated from cognitive, behavioural and psychodynamic perspectives; a case study of a 35 year old man with depression; a small scale service related project related to the evaluation of a consumer and referrer satisfaction survey of a local learning disability service; a single-case experimental design examining the efficacy of intervention with a 74 year old woman experiencing generalised anxiety, and a summary of an oral presentation outlining a systemic approach to family therapy. All names and identifying details have been changed to ensure client confidentiality. Volume II contains appendices of information relevant to the clinical practice reports.