Research has shown that numerous psychological changes can occur in and through collective action. Previous research on psychological consequences of participation in collective action has mainly focused on one change at a time and has rarely included a theoretical explanation for the change. The present study therefore investigates the range and possible connections between changes occurring in collective action. We interviewed participants (n = 28) involved in an environmental campaign in Sweden which included interaction with the police. Through thematic analysis of the data we found that the participants connected several psychological changes to aspects of their participation. Specifically, participants related these changes to two intertwined processes: intergroup interaction and intragroup interaction. We suggest that intergroup interaction (specifically conflict with the police outgroup) can affect intragroup processes (e.g., support and unity), which in turn can influence psychological change (e.g., empowerment and skills). Through the study, we develop and contribute to previous research by: 1) documenting a range of possible changes occurring through collective action participation, and 2) exploring the different psychological processes related to the changes. The implications of this research and future challenges are discussed in relation to developing the social identity approach.