This guide aims to provide practical tools to non specialists-essentially water resources planners, river basin managers, non-governmental organizations and private sector operators. It links the most recent practice on payments for hydrological services to current discourse on integrated water resources management and looks into the different aspects to consider when exploring the potential feasibility of establishing reward or payments for ecosystem services related to water security. Pay demystifies concepts and jargon, and through a series of tools, case studies and stories from around the world, describes pitfalls to avoid and provides hints to fill gaps in knowledge. It is based on a demand-driven approach, linking text, tools and illustrations to key questions emerging from current and potential practitioners.