This article discusses the concept and the practice of transdisciplinary research, including how it is conceived and implemented through the cooperation of different actors involved. With transdisciplinarity gaining recognition as an approach to addressing sustainable development challenges, the successful integration of various disciplines and actors in the process of knowledge generation becomes essential. Through the Cooperation and Development Center (CODEV), the Ecole Polytechnique Fédérale de Lausanne (EPFL) has promoted transdisciplinary research by proposing a space where North-South partnerships integrating academic and non-academic actors enable the expansion of appropriate technologies and innovations adapted to local societal contexts. This study examines five collaborative research projects conducted at the EPFL. By using an analytical framework consisting of design principles for ideal transdisciplinary research, we conducted semi-structured interviews with academic and non-academic members of the research projects to assess the degree of transdisciplinarity. This framework proved to be a useful tool for exploring transdisciplinary dynamics and assessing the effectiveness of joint knowledge generation. We found that the transdisciplinary cooperation involving different actors is not a linear process, as it depends on the social context in which the project is carried out and on the internal and the external organizational structure established for its implementation. We provide recommendations on how transdisciplinarity could be expanded through institutional support and its results could be effectively transferred into science and practice and discuss the implications for further studies in the conclusions.Sustainability 2019, 11, 4343 2 of 28 an ideal than as a reality [4,8,9]. Also, recent studies show that transdisciplinary research still faces a number of challenges that hinder the expansion of its practice and restricts its potential in addressing crucial matters of sustainable development [10][11][12][13].This article provides new empirical observations on the practice of transdisciplinary research, including how it is conceived and implemented and how the key actors involved are applying its results. The paper has two objectives. Firstly, it reviews the evolution of the definition of TD in sustainability science, differentiating it from the concepts of multi-and interdisciplinarity. Secondly, it contributes to the ongoing discussion on the added value of TD to research practice. The paper examines five projects conducted at Ecole Polytechnique Fédérale de Lausanne (EPFL) based on evidence collected through semi-structured interviews with academic and non-academic team members using an adapted analytical framework with a set of design principles for ideal transdisciplinary research [11,14]. The study shows how the practice of TD depends on the context in which research is carried out, on the organizational structure established for its implementation, and on the specific way in which the expe...