These audio files are part of a collection of the data supporting all results reported in Pranic et al., Vocal Ontogeny in Mus musculus. In Pranic et al., we characterize the developmental timing of the transition from infant distress calls to adult-like social calls in laboratory mice, Mus musculus. Infants of many species produce distress calls when in need of parental care. As they mature and gain independence from caregivers, juveniles stop producing infant calls and begin producing adult-like vocalizations in a variety of species-typical contexts. Neonatal mice (Mus musculus) produce “isolation” ultrasonic vocalizations (USVs) when separated from the nest, and in contrast, adolescent and adult mice produce “social” USVs during interactions with conspecifics. Although this transition in vocal behavior is known to occur, its developmental timing remains poorly described. In the current study, we performed longitudinal measurements of mouse USVs to establish the age at which juvenile mice begin producing social USVs. Every 4 days (postnatal day (P)12-P28), USVs were first recorded from individual mice in solo sessions to establish rates of isolation/spontaneous USVs and then were recorded again during interactions between same-sex and opposite-sex pairs of age-matched, socially novel (non-littermate) C57BL/6J mice. We report that juvenile mice begin producing social USVs earlier than previously reported, at ages P20-P24. Moreover, although these early social USVs are produced at low rates compared to adult social USVs, they are nonetheless temporally coordinated with active social interaction. Our characterization of the timing of the transition from isolation USVs to social USVs forms a foundation to investigate brain mechanisms that enable the context-dependent regulation of vocal communication over development.