Transdisciplinarity means bridging the gap between science and society. Facing the complex transformation challenges and developing sustainable development solutions, it gained more and more awareness in academic institutions to establish it as a research principle for creating new integrated knowledge and fostering transformation in science and society. What is transdisciplinarity as a research mode, how do we understand it, and how is it related to sustainable development? With a common understanding in the ENHANCE Alliance, we built a framework for transdisciplinary research processes and integrated knowledge exchange between science and society. As the ENHANCE universities each have their own organisational structure and culture, a shared and broad understanding of transdisciplinarity is key to foster the institutionalisation of transdisciplinarity.