To solve societal, sustainability-related issues, higher education requires new and innovative didactical concepts in learning. We introduce the concept of transdisciplinary-CBL (T-CBL) to explicate the role of diverse disciplinary and extra-academic actors in learning processes where students work in teams to co-create innovative solutions to societal challenges. To increase our understanding of how students learn from different actors in T-CBL, we used a survey, semi-structured interviews and sociograms to elaborate the nature of interactions with and the value students ascribed to these actors. The results show that students learn from a wide variety of actors in T-CBL. Extra-academic actors help by contributing expertise and informing solution pathways, whereas friends and family provide emotional support. T-CBL results in specific learning gains including perspective-taking. The results offer a picture of T-CBL as social learning in which students interact with networks of actors from which they learn ‘on-demand’.