Any analysis of health financing issues has to begin with sound estimates of the level and flow of resources in a health system, including total levels of spending, the sources of health expenditures, the uses of funds in terms of services purchased, and in terms of who purchases them. The analysis should also aim at understanding how these resource flows are correlated with health system outcomes, including those of improving health, reducing health inequalities, and reducing the incidence of catastrophic health expenditure. National Health Accounts (NHA) provide a framework to collect, compile, and analyze such data on all types of health spending in a country--and so create a robust evidence base for policy making. Although NHA data delineate the key financial metrics of a health system, the collection of these data have not been institutionalized in most developing countries. The root problems are often the same: insufficient resources to collect, collate, analyze and produce information on spending; poor development of health and other information systems; low levels of local capacity to interpret information to meet policy needs; and inadequate demand for data within countries. Furthermore, in many low- and middle-income countries, NHA activities have been conducted as ad hoc, donor-driven initiatives. Since 2008, the World Bank has been coordinating a global initiative to identify bottlenecks to the institutionalization of NHA, and to learn lessons in countries at different stages on the journey towards this institutionalization. The focus has been less on the production of NHA and more on its relevance as a tool to enable policy makers develop and implement evidence-based decisions, and better measure the impact of health reforms, especially those related to health financing. This report has been developed through a consultative process, involving experts and policy makers from more than fifty low-, middle- and high-income countries, large and small, in all corners of the world, development partners and World Bank staff globally. The report represents a synthesis of lessons learned from country experiences and is intended to serve as a strategic guide to countries and their development partners as they design and implement their strategy to develop nationally relevant and internationally comparable data, collected in a routine and cost-effective manner.