Quality assessment in health care is bedevilled with measurement problems. The measurement of output, or more strictly the agent’s effort in producing output, is particularly difficult. Quality can be measured in terms of the quality of inputs, processes, or outcomes. Input quality measurement, for example, would involve assessing the capabilities and training of the labour force, the standard of the capital facilities and equipment, and the input mix. Such an approach is often taken by health care regulators seeking to maintain a register of qualified providers. Process quality measurement, however, would involve assessing whether agents are performing actions that are most likely to generate good quality outputs. In health care, this might involve assessing whether providers are following best-practice guidelines and offering patients effective treatment regimes. Finally, quality output measurement would focus on the benefits that have been achieved for patients, regardless of how they have been achieved. Such benefits should include gains in survival and quality of life and increasingly capture patients’ experience of using health care services.