An age-old Sanskrit proverb says: 'my enemy's enemy is my friend'. Yet, in many civil wars, coethnic armed groups rebelling against the same government end up fighting each other. Why don't ethnic solidarity ties prevent this apparently self-destructive strategy? Pischedda argues that ethnic parochialism does not travel to the group level: coethnic groups aspire to control the same population and know that they could easily absorb the resources of defeated coethnic rivals, in turn improving their chances against the government. This competition generates a mix of expansionary ambitions and fear induced by shared ethnic identity. Usually, these conflictual goals are silenced by the overwhelming threat posed by the government. Yet, when the threat is less acute, coethnic groups may launch a 'hegemonic bid' to eliminate coethnic competitors (window of opportunity). Alternatively, when the costs of inter-rebel war are high but are expected to increase further, groups may attack coethnic rivals in a 'gamble for resurrection' aimed at preventing their relative decline (window of vulnerability). Pischedda tests this logic of coethnic conflict via process tracing on insurgencies in Iraqi Kurdistan and in Eritrea and Tigray. Chapter 5 extends the analysis to conflicts in Lebanon, Sri Lanka and Syria. Finally, a statistical chapter tests the theory's implication that coethnic groups are more likely to fight each other than non-coethnic ones. While the various chapters are not fully harmonized in a 'mixed methods' design as the author claims, they provide plenty of evidence in support of the 'windows' logic. By explaining the timing of inter-rebel war, Conflict Among Rebels represents a significant contribution to the burgeoning literature on rebel fragmentation and in-fighting.