Groundwater allocation determines who is able to use groundwater resources, how, when and where. It directly affects the value (economic, ecological, socio-cultural) that individuals and society obtain from groundwater, today and in the future. Building on the 2015 OECD publication Water Resources Allocation: Sharing Risks and Opportunities, this report focuses on groundwater and how its allocation can be improved in terms of economic efficiency, environmental effectiveness and social equity. Drawing on an analysis of groundwater's distinctive features and nine case studies of groundwater allocation in a range of countries, the report provides practical policy guidance for groundwater allocation in the form of a "health check". This health check can be used to assess the performance of current arrangements and manage the transition towards improved allocation.