It has now been 5 years since most of the countries of the world committed to the policies and programs for environmentally sustainable development laid out at the Rio Earth Summit in Agenda 21. Along with other international agencies, the World Bank has sought to be an active partner with its client countries in implementing the priorities set at Rio. While the past 5 years have brought some progress, it is not as much as was expected, and certainly less than what was hoped for. Furthermore, what has been invested has not been used as cost-effectively as it could have been. This volume documents the active role of the Bank in assisting its clients to work toward the goals laid out at Rio. Part I takes a broad perspective by assessing some of the greatest challenges for the future and laying out six principles to guide our thinking: 1) mainstreaming sustainable development; 2) integrating social and cultural dimensions; 3) investing in effective partnerships; 4) building and sharing knowledge; 5) measuring progress differently; and 6) mobilizing financial resources. Part II of the report addresses the majority of the chapters of Agenda 21 in turn. It provides concise reviews of progress since Rio and related World Bank activities, lessons learned, and challenges and prospects for the future.