Studies of communication in early infancy and childhood have highlighted the significance of rhythm, sound and music for emotional and social development. There is, however, little detailed empirical data on the emergence of naturalistic music-related behaviour by children in the early years. The aim of this work is to examine instances of musicality with respect to their form and/or function and to trace out developmental indices of musically related behaviours and competencies. Employing a single-case study approach, this paper documents the emergence of one child's musicality between the ages of 1 year, and 3 years 10 months. From a data corpus of video-recordings, 33 examples of musicality, representing 20 time periods, were examined and categorized. In order to examine specific instances, ethnomethodologically informed conversation analysis was used to consider examples in more detail. Beyond indicating what conversation analysis might bring to the study of musical behaviour in context, the results highlight certain interrelationships between musicality, early word use, interpersonal skill and narrative development. Distinct phases--social-affective followed by "song-word" play and finally narrative-related musicality--were identified in the data. Concluding comments touch on the significance of emerging musicality for social and cognitive development. (Contains 4 tables and 12 notes.)