Almost all living things communicate, yet only humans have language. The question of how this came to be has puzzled scientists and philosophers for centuries. In more recent years, researchers have looked to primate communication systems in order to gain insights into the evolutionary origins of language. While many studies have successfully identified language-like features in adult primate communication systems, the parallels between human and non-human primate vocal ontogeny are poorly understood. In this thesis, I aimed to address this issue by examining the process of vocal ontogeny in chimpanzees. In my first empirical study, I examined the ontogeny of the acoustic structure of the vocal repertoire. It was found that the chimpanzee vocal repertoire in the first 10 years of life did not increase in the number of call types, but became increasingly acoustically graded. In my second empirical study, I examined the ontogeny of patterns of vocal production and function, finding that from infancy chimpanzee grunts express a wide range of affective states, and later during the juvenile period these calls show signs of functional flexibility. Such patterns were not observed for any other call types. Finally, in my third empirical study, I examined the ontogeny of directedness and engagement during vocal communication. It was found that chimpanzees routinely showed directedness and engagement during vocal communication, directedness generally increased during ontogeny, and was associated with a higher probability of eliciting responses from social partners. Overall, the findings of this thesis suggest that while acoustically speaking, chimpanzee vocal ontogeny is rather different to human vocal ontogeny, chimpanzee vocal ontogeny is characterised by communicative capacities that are important precursors for language ontogeny (i.e. flexible vocal production, functional flexibility, directedness, and engagement). In turn, this might suggest such capacities were also important phylogenetic precursors to language.