Developmental transitions, such as the onset of walking, are associated with changes in a broad range of domains, including language development and social interactions. This study used a full-day home observation recording to compare the language environment of age-matched crawling and walking infants. Central to the study was exploring how the language environment related to vocabulary development of each locomotor group. Adult words, infant vocalizations, and parent-child conversational turn-taking were positively associated with infant vocabulary development, but only for walking infants. These findings provide further evidence for the integrated nature of infant locomotion, language development, and the social and linguistic environment.