Underlying the emerging interest in the role of rivalry processes as antecedents to interstate conflict is the simple idea that conflict within the constraints of rivalry works differently than conflict outside of rivalry. In this article, we inspect the concepts of protracted conflict, as developed within the International Crisis Behavior (ICB) project, and rivalry, and discuss some of their applications to crisis escalation. The protracted conflict and rivalry concepts are not identical, but they do overlap in terms of their emphases on historical context, serious goal incompatibilities, and stakes that might be resolved coercively. Developing an argument for the concept of rivalry possessing fewer limitations than protracted conflict, we proceed to analyze and test the interaction between rivalry and other variables, again making use of an ICB escalation model, when predicting crisis escalation to war. Throughout, our basic question concerns what role interstate rivalry plays in crisis behavior. Are the crises of rivals more lethal than those of non-rivals? If so, can we pinpoint why that is the case? We find that rivalry not only makes escalation more likely, but also significantly interacts with more traditional predictors of conflict, such as capability ratios, the number of actors in a crisis, democracy, and the issues under contention.