How do institutionalized political parties affect civil conflict across regimes? We examine two competing explanations concerning the link between party institutionalization and civil conflict. On the one hand, more institutionalized political parties offer stronger channels for patronage, communication, and representation, which should serve as a mechanism for resolving conflict in both non-democracies and democracies alike by improving coordination among domestic actors. At the same time, however, more institutionalized parties may exacerbate civil conflict if they support interest aggregation and mobilization against a backdrop of limited freedoms. In exploring the relationship between party institutionalization and civil conflict across regimes, we take into account both nonlinearities as well as historical effects.