OBJECTIVE: To review the evidence on commissioning schemes involving clinicians in the United Kingdom National Health Service, between 1991 and 2010; report on the extent and impact of clinical engagement; and distil lessons for the development of such schemes both in the UK and elsewhere. METHODS: A review of published evidence. Five hundred and fourteen abstracts were obtained from structured searches and screened. Full-text papers were retrieved for UK empirical studies exploring the relationship between commissioners and providers with clinician involvement. Two hundred and eighteen published materials were reviewed. RESULTS: The extent of clinical engagement varied between the various schemes. Schemes allowing clinicians to act autonomously were more likely to generate significant engagement, with 'virtuous cycles' (experience of being able to make changes feeding back to encourage greater engagement) and 'vicious cycles' (failure to influence services generating disengagement) observed. Engagement of the wider general practitioner (GP) membership was an important determinant of success. Most impact was seen in GP prescribing and the establishment of services in general practices. There was little evidence of GPs engaging more widely with public health issues. CONCLUSION: Evidence for a significant impact of clinical engagement on commissioning outcomes is limited. Initial changes are likely to be small scale and to focus on services in primary care. Engagement of GP members of primary care commissioning organizations is an important determinant of progress, but generates significant transaction costs.