In Skinner's analysis of verbal behavior, three categories of environmental control over instances of verbal behavior appear to be relevant to the study of infant vocal development: the mand, the tact, and the echoic categories. Procedures used in the remediation of language deficiencies and procedures found in work in the area of language learning and communication may also be relevant to the functional analysis of the acquisition of vocal behavior by infants. Topographically, infant vocal development progresses from diverse and indiscriminant vocal behavior to differentiated and discriminated vocal/verbal skills during the first year of life. One valid operant explanation of the functional development of infant vocal behavior is that the infant's differential responding to the vocal environment she/he is experiencing is consequated with homeostatic reinforcers which are in turn paired with social consequences parents typically provide. As a result of experiencing this pairing process intensively, the tactile, visual, and auditory stimulation provided by the parents take on discriminative as well as reinforcing properties for the infants. Once established and maintained as a discriminative and reinforcing stimuli, these adult behaviors could function to set the occasion for and consequate approximations to adult behavior by the infants. This explanation would account for the manding, echoic, and tacting functions that appear to be characteristic of much of the first year of the infant's vocal behavior. (JMB)