Language and other forms of communication are inherently ambiguous and therefore require some form of common ground to specify the intended meanings of utterances. Theoretical accounts usually focus on interactions between adults and consider recursive mindreading a prerequisite to establishing common ground. Contrasting these accounts, in this article, we offer a developmental perspective on common ground. We propose that instead of using recursive mindreading, infants rely initially on the expectation that communicative partners act rationally in light of previous interactions, which serves as a starting point for common ground to develop. We describe the changing role of common ground across development. Initially, common ground constrains the meaning of ambiguous communicative acts and facilitates children's acquisition of language. Later in development, common ground makes communication efficient by helping speakers coordinate their actions and intentions, and eventually arrive at recursive mindreading.