Collective intentionality lies at the heart of solidarity and social action. Collective intentions refer to thinking in a “We-mode” oriented toward the social group, contrary to individual-oriented thinking in “I-mode”. Theories in philosophy and sociology have long recognized the importance of collective intentions for solidarity. Yet, less is known about how collective intentions affect solidarity on different levels of analysis. The dissertation aims to introduce collective intentions to sociological research and to close the research gap by studying the relationship between collective intentions and solidarity. In study I, we study collective intentions in small group dynamics via an online experiment. We find that collective intentions are strongly related to solidarity and emerge through social interactions in groups. Study II uses computational text analysis and qualitative in-depth reading to investigate how US governors draw on collective intentionality to mobilize people during the COVID-19 pandemic. We find that political leaders evoke collective intentionality by emphasizing unity, vulnerability, action, and community boundaries. While Democratic governors emphasize a shared agency between government and citizens, Republican governors highlight more of a top-down approach to governmental action. Similarly, study III examines political leaders’ use of collective intentionality and the distribution of governmental and civic roles across nine countries during the coronavirus pandemic. While all political leaders highlight the importance of unity, solidarity, and social action in public speeches, I find that political leaders’ narrative on the distribution of governmental and civic roles does not align with existing patterns across party lines. Finally, study IV focuses on whether politicians’ use of collective intentionality in times of crisis influences peoples’ solidary intentions and behavior in an online experiment. We find no evidence that collective intentionality in political speeches affects solidarity, suggesting that collective intentionality cannot be built through speech acts only, without being based on shared we-experiences, community, and trust. Taken together, the studies in this dissertation contribute to research on collective intentionality and solidarity. Within social group interaction, collective intentionality fosters social cohesion and solidarity. In crises, collective intentionality provides insight into the group boundaries, responsibilities, and distribution of roles.