A study has been made on the infant, Sarah, from age 1 month up to 18 months. The main interest of the study was concerned with her phonetic and phonological development in the stages of: Crying, Babbling and First Words. As to the first stage, Crying, I intended to give as much coverage as possible to my subject's crying in the first six months of her life, attempting to analyze and explain it, making clear any differences in structure and content. According to the contextual situations in which they were produced, cries were categorized as: 1) Call Cries, 2) Protest Cries, and 3) Non-call Cries. Vocalizations included in the above categories were tested according to their manner of phonation, temporal patterning and melodic patterning. As to the Babbling stage, Sarah's babblings were tested against the following issues: - Variety of sounds produced, - Relation between babbling and speech, - Are babblings meaningless and playful?, and - Function. Finally, the child's first words were tested against the following issues: - Appearance of the first word, - Holophrases, and - Overextension.