While peace processes increase the likelihood that a civil war is resolved, they can also complicate peace by increasing the risk of rebel fragmentation. In this article, we argue that negotiations exacerbate pre-existing structural and substantial divisions within rebel organizations, therefore increasing the likelihood of a rebel split. More specifically, we put forward a theoretical framework that specifies why factions within a rebel group may disagree with the onset of negotiations, the conclusion of a peace agreement, or the implementation of an agreement-and thus break away during the peace process. We empirically assess the merit of this framework by systematically comparing the impact of these phases in a peace process on the fragmentation of rebel organizations. Using data that more accurately reflect the moment a rebel split takes place than earlier studies, we find that peace processes have a greater substantial impact on rebel fragmentation than previously assumed.