On the road to the 10th anniversary of the OECD Principles on Water Governance, the Handbook of What Works aims to further drive their implementation at sub-national level (e.g. municipal, regional and basin) through a compilation and analysis of evolving water governance practices. Building on a compendium of 52 water governance practices, the Handbook illustrates how cities, regions and basins in both OECD member and non-member countries have designed and implemented effective, efficient and inclusive water governance systems. It identifies common pitfalls to be avoided when designing and implementing water policies across levels of government, draws lessons from both successful and challenging implementations of each Principle and highlights the potential for replication of these practices to other contexts.