Regime type is an important variable in international relations. Numerous scholars have theorized its effects on actors’ crisis behavior and outcomes. Despite regime type’s importance, the literature has not focused on the role its uncertainty might play in interstate politics. This is in stark contrast to the scholarly attention given to uncertainty about other similarly important variables like actor capabilities, intentions, or fighting costs. In this paper, we aim to address this gap in the literature by providing a theory of regime uncertainty’s effects on conflict, and developing a novel measure of uncertainty about regime type in interstate relations to test our hypotheses. We find that regime uncertainty breeds caution rather than conflict: higher uncertainty about the opponent’s regime type makes conflict initiation and escalation less likely in disputes, and dyads with more uncertainty are less likely to experience conflict onset.