The sound of speech, independent of the words, is a rich channel of information. Because different communicative interactions pose different kinds of problems for those involved, the form that communication takes often depends on the specific communicative problem that must be solved. I will present two examples from my own research of how the acoustic form of speech facilitates the communicative goals of interlocutors: communicating intentions to preverbal infants in the case of infant-directed speech, and how vocal cues of ovulation and attractiveness manifest themselves in women’s voices. I will conclude with thoughts about how form-function analyses can illuminate a host of phenomena in the study of communication and cognition.