Theoretical models are often used to analyze reproductive conflicts in animal societies; for example, by determining the different sex-allocation optima of queen and workers. But who is in control (queen or workers, dominant or subordinate) is normally an implicit or explicit assumption of the model. Here, we introduce the concept of power (the ability to do or act in a situation in which conflict over reproduction exists) and argue that the relative power of conflicting individuals or groups of individuals (e.g. the workers or subordinates) within a society can complement theoretical predictions to provide a deeper understanding of reproduction in animal societies. We also show that power involves both general principles, such as differences in the quality of the information available to conflicting parties, and idiosyncrasies of the biology of different taxa, such as viviparity versus oviparity. These idiosyncrasies can occur at any taxonomic level, from a single species to an entire order or class, and are often crucial for understanding the balance of power among conflicting parties.