Water resources allocation determines who is able to use water resources, how, when and where. It directly affects the value (economic, ecological, socio-cultural) that individuals and society obtain from water resources. This report overviews how allocation works in a range of countries and how the performance of allocation arrangements can be improved to adjust to changing conditions. Capturing information from 27 OECD countries and key partner economies, the report presents key findings from the OECD Survey of Water Resources Allocation and case studies of successful allocation reform. It provides practical policy guidance for water allocation in the form of a "health check", which can be used to assess the performance of current arrangements and manage the transition to improved regimes.