Transdisciplinarity as a mode of addressing sustainability challenges was a guiding principle in establishing Germany's first Faculty of Sustainability at Leuphana University of Lüneburg in 2010. The different study programs offered by the Faculty embody this principle in different ways, but they all rely on the idea that it is important for students to constitute learning spaces in-between established scientific and societal fields. Students have to identify boundaries, understand different cultures of knowing and practice, and conduct integrative research by bridging gaps between knowledge fields, practices and related values as well as interests and objectives. In this paper, we focus on one module in the Master's Program in Sustainability Science and present how students constitute and learn in these in-between spaces through boundary-work with the aim to gain capacities required to contribute to sustainability transitions.