Which factors make it more likely that environmental nongovernmental organizations (ENGOs) exist in autocracies? Several studies addressed this question before but might suffer from two shortcomings. First, the more general literature on social movements treats nonstate actors as a closely related characteristic of democracies. This neglects, however, that ENGOs might exist in autocracies as well. Second, the more specialized literature on comparative environmental politics examines ENGOs in autocratic regimes but rather focuses on single case studies. Despite fascinating insights, we thus lack a comprehensive theory on why ENGOs might exist in different types of dictatorships. In light of this, the following research adds to this by developing a theory that is based on the political opportunity structures (i.e., degrees of repression) in different autocratic typologies. The empirical analysis using data on 71 autocracies from 1973 to 2003 emphasizes that ENGO existence strongly differs across single-party regimes, monarchies, military regimes, and personalist dictatorships.