Practice-based commissioning, in which general medical practices are provided with an indicative budget with which to commission services for their patients, was introduced into the National Health Service from 2004 onwards in order to generate front-line clinical engagement with the commissioning process. The aim of this research was to describe and analyse the rationale for, and implementation and outcomes of, practice-based commissioning in England over a period of 27 months. Information for the study was gathered through relevant documents, semi structured interviews with civil servants involved in establishing practice-based commissioning, a national questionnaire survey of all 152 primary care trusts (PCTs) in 2007, case studies of 5 'early adopter' consortia in 3 PCT sites in 2007, and case studies of 12 consortia in 7 PCT sites in 2008/9. The case studies included interviews, formal observations and analysis of documentation. This paper describes the study and its results, including factors that affect practice-based commissioning outcomes. It also discusses the main policy implications, noting that the policy is still quite new and requires time and resources to develop its full potential, and makes suggestions for further research.