Competition law enforcement has spread worldwide, providing potentially a rich dataset for assessing its effects. At the same time, Governments everywhere are increasingly interested in measuring the results of their policies, and are more than ever concerned about value for money as budgets come under pressure. Yet performance measures adopted by competition agencies rarely even mention the outcomes – such as growth – in which policymakers are interested. The OECD has embarked on a three-year project to collate and advance understanding of how the application of competition law and policy affects outcomes, at the micro and macro levels. I will talk about the policy environment and some possible uses of better measures of competition and its effects. I will give a personal overview of the literature as I see it including – crucially – where the gaps are. This is intended to lead to a dialogue with interested researchers about where further research is needed and how it might be done.