Evidence shows that addressing real-world societal problems can be best achieved through collaborative research where diverse actors contribute different kinds of knowledge. While the potential benefits of transdisciplinary (TD) research are widely recognized, its implementation remains a challenge. In this article, the authors develop a framework that supports reflection and co-learning. Their approach fosters monitoring of the collaboration processes, helps to assess the progress made and encourages continuous reflection and improvement of the research processes. The TD co-learning framework has four dimensions and 44 criteria. It is based on a substantial literature review and was tested in the ROBUST project.