The science-policy interface is critical to the design and implementation of water policies. In theory, scientists provide policy makers with robust facts and data that can help guide decision making, and lessons from the political economy of reforms can push scientific boundaries further to trigger further research for wise solutions. While evidence-based policy is obviously desirable, in practice such a connection is not always straightforward. Another assumption behind the science-policy gap is the discrepancy between scientists and policy makers in terms of culture, process, timing, language and expected outcome. This book tries to reconcile this discrepancy through a multi-stakeholder approach to authoring its different articles. This joint initiative between the OECD - particularly its Water Governance Initiative - and the International Water Resources Association seeks to provide a canvas for grounding water policy in science, and vice versa. The objective of this book, devoted to the OECD Principles on Water Governance, is to use the OECD Principles as a common thread across the articles to draw lessons from theoretical work and practical experiences in water governance reforms; but also to only feature papers authored by groups of diverse stakeholders from different institutional backgrounds. This book was originally published as a special issue of Water International.