This article analyzes the physiological and psychological mechanisms of speech development in the first year of a child's life. The maturation of the central nervous system and peripheral speech apparatus, the role of the initial sound reactions - screaming, cooing, gurgling - in the process of speech ontogenesis is highlighted on the basis of scientific sources. The formation of speech is explained by the development of auditory memory, differential perception of sounds, intonational means and the increased need for communication. The study comprehensively examines the stages of phonetic and intonational development of a child's speech, their neurophysiological foundations, and individual differences in speech development. The article substantiates the crucial importance of the early periods of speech ontogenesis in the formation of the child's future speech and cognitive competencies. Psychological, pedagogical and methodological literature on the topic of stages of speech development in ontogenesis, anatomical and functional features of the central nervous system and peripheral speech apparatus has been studied and analyzed.