This chapter summarises the main findings of this project on geographic variations in health care use across and within a number of OECD countries, and identifies a range of policy levers that can be used to reduce unwarranted variations, defined as variations that cannot be explained by patient needs and/or preferences. This summary draws mainly on the 13 national reports from Australia, Belgium, Canada, the Czech Republic, Finland, France, Germany, Israel, Italy, Portugal, Spain, Switzerland and the United Kingdom (England) which are published in the following chapters. The analysis focusses on a selected set of health care activities and procedures, including hospital medical admissions and some high-volume and high-cost diagnostic and surgical procedures. The results show that large variations in health care use persist, across and within countries, even after taking into account differences in demographic structures. While the analysis in this study does not allow to determine precisely how much of these variations are unwarranted, some of these variations are too large to be explained solely by patient needs and/or preferences. A number of policy interventions have been used in different countries to address unwarranted variations in health care use, including public reporting, the development and monitoring of clinical guidelines, the diffusion of decision aids for patients to complement the information they receive from physicians, and changes in financial incentives to try to reduce the inappropriate use of certain procedures.