This tool book reflects the growing awareness that ecosystems are important to water management. In the past, we did not realize the many benefits of ecosystems and consequently ignored them in our management decisions. The result was environmental degradation, oftentimes leading to increased poverty for water- and wetland-dependent communities. Now, we are increasingly recognizing that ecosystems play a very important role in the demand and supply side of water: ecosystems use water, regulate water supply, and provide a range of products and services on which people depend. Moreover, we increasingly have, at our disposal, the policy frameworks, the tools and the willingness to put that insight into practice. Economic valuation of ecosystem services is an important tool for effective and efficient water management as it offers us a way to make the roles of healthy ecosystems visible and to factor these into decision-making. It tells us what may be lost due to management interventions, and helps identify compensation measures. In other cases, it may lead to investments in conservation measures, such as forest management or wetland protection, and realization of sustainability of new infrastructure.