This report is about building institutions that support markets which promote growth and reduce poverty. It analyzes the myriad of institutions--formal and informal, public and private--that people build and use to undertake activities that maximize returns and to manage risk in markets. These institutions range from unwritten customs and traditions to complex legal codes that regulate international commerce on the cutting edge of technology. Some developing countries have been able to harness such market-supporting institutions to improve the welfare of their people, but others have not yet achieved the same degree of success. Drawing on a wealth of research and experience from inside and outside the World Bank, this 23rd edition of the World Development Report moves toward a deeper understanding of market-supporting institutions and a better appreciation of how people can build such institutions. Building Institutions for Markets takes a two-step approach to institutional development. First, it contends that what is critical is focusing on the functions that market-supporting institutions provide and how they provide it rather than on particular structures. Looking at institutions in terms of the functions they provide rather than in terms of their structures helps identify institutional gaps. Second, after identifying the institutional gap, the next step is to build the needed institution. The report goes beyond the recognition that one size does not fit all to develop an understanding of how to think about designing effective institutions in a particular context. Building Institutions for Markets includes Selected World Development Indicators, an essential reference on recent trends in development. Altogether, the report offers valuable insights and vital guidance for policymakers, researchers, and anyone with an interest in development.