This report identifies the issues arising from the development of a multilateral instrument that modifies bilateral tax treaties. Without a mechanism for swift implementation, changes to model tax conventions only widen the gap between the content of these models and the content of actual tax treaties. Developing such a mechanism is necessary not only to tackle base erosion and profit shifting, but also to ensure the sustainability of the consensual framework to eliminate double taxation. This is an innovative approach with no exact precedent in the tax world, but precedents for modifying bilateral treaties with a multilateral instrument exist in various other areas of public international law. Drawing on the knowledge of experts in public international law and taxation, the Report concludes that a multilateral instrument is desirable and feasible, and that negotiations for such an instrument should be convened quickly.