The Convention on the Protection and Use of Transboundary Watercourses and International Lakes (Water Convention), hosted by the United Nations Economic Commission for Europe (UNECE), requires Parties to establish and implement joint programmes for monitoring transboundary waters, to carry out joint or coordinated assessments of the conditions of transboundary waters and to exchange data and information to enable sustainable management and protection of shared water resources. The Updated Strategies for Monitoring and Assessment of Transboundary Rivers, Lakes and Groundwaters provide strategic guidance on monitoring, assessment and data sharing in a transboundary context, building on the global experience on these issues. The publication is intended to assist policy and decision makers, representatives of joint bodies for transboundary water cooperation, and water managers responsible for establishing and carrying out cooperation between riparian countries, in operationalizing cooperation over transboundary waters. It aims to contribute to the effective implementation of the Water Convention and improved transboundary water cooperation worldwide.