Health data constitutes a significant resource in most OECD countries that could be used to improve population health, the quality of health care and the performance of health systems. Rising levels of chronic diseases; concerns about the quality and safety of patient care; the need to assure value for investments in health care; and the need to allocate health resources wisely; are all too important to be left without good evidence for decision making. This book, based on studies of 19 countries on the development and use of personal health data and of 25 countries on development and use of electronic health record systems, includes results showing good practices, new opportunities and data privacy protection challenges. It finds that well-intended policies to allay concerns about breaches of confidentiality and potential misuse of personal health data may be limiting data use, but that the next five years appear promising, in terms of both the number of countries that plan to implement national electronic health record systems and the number that consider it likely that data from these systems will be used for some aspects of health care quality monitoring. They also appear promising for the further use of existing personal health databases and for the linkage of multiple data sources to generate new evidence.