At its eight session, the Meeting of the Parties to the Convention on the Protection and Use of Transboundary Watercourses and International Lakes (Water Convention) decided to develop a handbook based on existing practices covering the key aspects of equitable and sustainable allocation of water in the transboundary context, addressing both surface waters and groundwaters, and also environmental flows (programme area 3, activity 3.3). Work began in 2019 on developing the Transboundary Water Allocation Handbook, which will provide a global review of water allocation arrangements in transboundary basins. Illustrative case studies from around the world will highlight diverse transboundary allocation practices, challenges and lessons learned. The development of the Handbook is being supported by an Expert Group to provide guidance and oversight on the structure, substantive content and illustrative case studies. The Handbook will reference relevant tools and information resources and examples of: (a) the key elements (e.g., institutional framework, data sharing) for agreeing on water allocations; (b) options and approaches that can be followed technically and legally; (c) relevant considerations in designing a process to agree on water allocation; and (d) the benefits that can be drawn from agreeing on water allocation. The experience in implementing existing allocation arrangements as well as limitations of water allocation will also be included.