Inter- and transdisciplinary research projects bring with them both challenges and opportunities for learning among all stakeholders involved. This is a particularly relevant aspect in social-ecological research projects, which deal with complex real-world systems and wicked problems involving various stakeholders’ interests, needs, and views, while demanding expertise from a wide range of disciplines. Despite its importance in such research efforts, the learning process is often not the primary focus of investigation and therefore the knowledge about it remains limited. Here, we put forward an analytical framework that was developed to assess the learning process of both the research team and other participating stakeholders within the scope of an international transdisciplinary project dealing with urban green and blue infrastructure. The framework is structured around five dimensions of the learning process: “Why learn?” (the purpose of knowledge generation and sharing); “What to learn about?” (the types of knowledge involved); “Who to learn with?” (the actors involved); “How to learn?” (the methods and tools used); 'When to learn?' (the timing of different stages). We developed an interview protocol to operationalize the framework and tested our approach through interviews with project researchers. Based on our empirical results, we draw main lessons learned that can inform other transdisciplinary projects. These include capitalizing on what already exists, addressing trade-offs inherent to different types of knowledge, fostering inter- and transdisciplinarity, engaging stakeholders, supporting a learning environment and fostering reflexivity. Besides the empirical insights and the lessons we present, the main contribution of this research lies in the analytical framework we developed, accompanied by a protocol to apply it in practice. The framework can capture the learning process taking place in transdisciplinary research more comprehensively than similar existing frameworks. The five intertwined dimensions it covers are essential to understand and plan such learning processes.