Around the world, intensifying demands for water resources, changes in the hydro-climatic cycle, and degrading water quality pose threats to human and ecosystems. These risks are particularly of concern in transboundary river basins, where coordination across international political boundaries adds complexity to already challenging governance issues. The effective production of scientific knowledge and incorporation of that knowledge into decision-making will be a critical factor influencing how such water-related risks are mitigated, as decision-makers respond to potential impacts and externalities that span sovereign countries. This pursuit will identify promising pathways by which science is developed and informs policy in transboundary basins. Using a multi-stage approach, we will harness the expertise of an interdisciplinary group of practitioners, policymakers, and academics who work in transboundary river basins and have been producers and/or users of knowledge and information in order to (1) delineate the scope of the science produced for; (2) depict the formal institutional mechanisms for incorporating science into decision-making in; and (3) identify example pathways for the use of science in three well-institutionalized transboundary water governance institutions spanning three continents: the International Joint Commission (North America), the International Commission for the Protection of the Danube (Europe), and the Mekong River Commission (Asia). Results from this synthesis will inform understandings of the science-policy interface in transboundary rivers and will provide lessons about actionable science for policy-makers to draw upon as they consider how to best develop and enable incorporation of science into decision-making.