Platforms are increasingly used to orchestrate interaction and cooperation among the diverse actors needed to address grand challenges. Empirical studies, however, remain limited in exploring the design and use of what we term grand challenge-oriented platforms to achieve societal outcomes. In this study, we investigate how grand challenge orientation influences the design, use, and evolution of digital platforms, with a particular focus on legitimizing processes towards ecosystem actors. Based on a qualitative study of the European Commission’s Mission “Climate Neutral and Smart Cities” and its supporting platform organization NetZeroCities, we identify key tensions in grand challenge-oriented platform legitimation. While a platform’s alignment with a higher-order purpose, like a grand challenge, attracts users, usability challenges often undermine its legitimacy, requiring participants to bypass the platform to achieve grand challenge-related goals. We also reveal that a grand challenge-aligned platform identity fosters collective action by aligning stakeholder behavior around a shared purpose. Through our findings, we present an informed theoretical model that makes two significant contributions. First, we advance understanding of how platform identity, shaped by societal missions, reinforces legitimacy through shared purpose and stakeholder alignment. Second, we contribute to the literature on collective action and grand challenges by theorizing how platforms used to address societal goals serve as organizing agents, enabling and sustaining collective action over time.
