Crying is a vital communication signal for the baby. Product of a complex physiological process, it reflects not only the organization and functioning of the cortical central nervous system and the function of sympathetic and parasympathetic autonomic regulation but also the integrity of three entities: the lungs responsible for ventilatory mechanics and respiratory rhythm, the larynx and its vocal cords as a phonatory organ, and the oropharyngeal tract guaranteeing the resonance of the sound emitted by the vocal cords. Crying is usually caused by pain, discomfort, hunger, or separation from parents or other caregivers. Crying carries essential information from birth, the expression of which depends closely on the neuroanatomical and functional brain integrity of the child. On a bioacoustic level, crying consists of sequences of complex acoustic signals produced by the vocal folds and filtered by the vocal tract. The vibration frequency of the vocal cords determines the cry's fundamental frequency f0 (and the harmonic frequencies), which is responsible for its more or less low or high pitch. Other acoustic cues also characterize each baby's cry.