Groundwater is a vital source for drinking water, irrigation, industry and the sustainability of wetlands, springs and river flows. In recent decades, groundwater use has increased tremendously. Climate change and population growth are likely to result in a further increase in groundwater use. To sustainably manage groundwater a good understanding of the resource and factors affecting it is crucial. Many actors have an impact on groundwater and to minimise disparity between those stakeholders it is important to provide stakeholders wide access to information on the resource. Assessing and sharing information on transboundary aquifers provides a particular challenge as it involves cooperation between countries which may have different approaches to assessing groundwater and different data protocols. A methodology is presented for the assessment of transboundary aquifers; it covers hydro(geo)logical, socio-economical, environmental, legal and institutional aspects. Results can be presented as indicators for comparative assessments of multiple aquifers. In-depth assessment at the aquifer level provides relevant information to develop specific management actions. To facilitate dissemination of results between (international) stakeholders, a webbased Information Management System has been developed, which gives access to thematic maps and underlying data, enabling stakeholders to perform their own analyses in support of sustainable groundwater governance.