Many biological processes have rhythmic organization, including the perception and production of music. Rhythms organize information that unfolds over time; they aid in parsing that information into meaningful hierarchical groupings; and the regularities of rhythms enable prediction of, and preparation for, when important information will occur in the future. Expressive deviations from isochronous timing convey emphasis, emotion, and meaning. Young infants are sensitive to timing and rhythm in music but these abilities become much more sophisticated during childhood. In the beginning, timing characteristics of infant-directed singing relate to the communication of emotional information. Through development, children become enculturated to the rhythmic structures in their environment, develop the oscillatory brain processes to link auditory and motor aspects of entrainment, become able to entrain movements to auditory rhythms, and use the synchronicity of movements between people to help make judgments about social relationships and who to trust and befriend.