The English NHS is currently organised around a split between the ‘commissioning’ and the ‘providing’ of health care. There has been considerable critical comment about commissioning, focusing upon perceived inadequacies of the regulatory structure and a perceived lack of competence of the managers concerned. In this paper, we use empirical data from two detailed studies of commissioning to propose a third explanation of the difficulties that have been observed in making commissioning work. We apply Scott's institutional analysis to the issue, arguing that far from reflecting managerial incompetence, some of the difficulties experienced are inherent in the normative and cultural/cognitive pillars of the NHS institution, so that there is a lack of ‘fit’ between commissioning and the institutional characteristics of the NHS. We conclude by exploring the potential impact of the latest round of NHS changes on this institution.