How does parent-infant interaction impact infant's communicative development? The aim of the studies presented here is to better understand the function of early social interactions in providing opportunities for vocal development and language learning. Parental behaviors that organize infant attention can create socially coordinated, aligned interactions in which attentional focus, object movements, and labeling are synchronized in ways that promote word learning. Alignment is a process in which communicators' production and comprehension of speech become coupled to establish common ground. By examining language development as an outcome of a socially embedded system of bidirectional feedback, the experiments presented in this thesis investigates how prelinguistic infants and their caregivers develop vocal alignment to support the emergence of mature communication. The research presented here: (1) investigates the constraints on socially guided statistical learning in influencing infants' learning of new phonological patterns from caregivers contingent responses to infant vocalizations; (2) determines the function of the infant's own object-directed prelinguistic vocalizations in facilitating the mapping of word-object associations; (3) examines the role of caregiver experience in responding to infant vocalizations; and (4) assesses the characteristics of infant vocalizations that elicit social interactions from caregivers. Taken together, the results of these experiments enhance our understanding of the cognitive mechanisms by which communicative alignment influences infant language development. i