TOURSUS-EU is designed to contribute to the definition and transition toward a more sustainable tourism model, one of the most pressing challenges for the European Union. Recognizing the critical effects of mass tourism, the project proposes a framework for measuring and understanding its effects on local economies, societies, and environments. The project centres on three major UNESCO World Heritage cities: Venice (Italy), Lisbon (Portugal), and Split (Croatia), all of which are emblematic cases of overtourism. Specifically, the project aims to deliver a framework for identifying key risk indicators in tourism destinations, serving as early warning signals for necessary policy interventions; predictive models for sustainable tourism growth, designed to evaluate influencing factors and project future scenarios; and a strategic guide for sustainable tourism management, outlining actionable recommendations for local authorities, planners, and stakeholders to mitigate overtourism and promote long-term resilience. Potential Impacts can be envisioned at different scales. These include, on a local level, an improved capacity of municipal authorities to monitor and manage tourism-related pressures and the empowerment of local communities through informed planning and stakeholder engagement. On national level, the project contributions can enhance the preservation of cultural and natural heritage sites and contribute to the formulation of evidence-based tourism policies, while also strengthening the collaboration and sharing of best practices between cities. At the level of the EU, TOURSUS-EU generates impact by contributing to a replicable model for sustainable tourism assessment across member states and delivering data-driven insights to inform European tourism strategies and funding priorities. Finally, on a global level, the project demonstrates scalable tools and approaches for UNESCO sites and global tourist destinations with the potential to influence international standards and frameworks on sustainable tourism. It strengthens the role of European research and policy leadership in global sustainability debates by aligning academic outcomes with practical policy needs, contributing to more resilient, inclusive, and sustainable tourism futures.