This chapter investigates cross-national variation in pro-environmental activism across 23 European countries at 2 time points—2010 and 2020 (37 cases in total). We employ fuzzy-set Qualitative Comparative Analysis (fsQCA) to examine how subjective cultural (values, attitudes, orientations) and objective institutional (economic, social, political) conditions shape levels of activism in the analysed countries. Pro-environmental activism, measured through four types of environmentally friendly public behaviour, showed considerable variation across countries and periods. Western and Northern European countries generally exhibited higher levels of activism compared with Central, Eastern, and Southern Europe, consistent with earlier findings. High environmental awareness emerged as a necessary, though not sufficient, subjective cultural factor, requiring additional conditions such as strong pro-environmental efficacy or high uncertainty avoidance. On the objective institutional side, a large salariat class and high Human Development Index values were important but effective only in specific configurations, often in combination with relative wealth or robust participatory democratic institutions.