Early mother-infant coordinated interactions play a critical role in infant development. The present study describes the development of the dyadic coordination of vocalization and gaze behavior between mothers and infants over the first year of life. In addition to describing developmental trajectories of behavior, the study contributes to our understanding of dyadic coordination by investigating how different measures of coordination relate to one another and how individual behaviors relate to dyadic coordination within the vocal and gaze domains. Thirty dyads were recorded playing together with a standard set of toys when infants were 3, 6, 9, and 12 months of age, and mother and infant vocalization and gaze behaviors were coded from these videos on a moment-to-moment basis. Coordination was analyzed using both cross-recurrence quantitative analysis and event-based measures of analysis. Hierarchical linear modeling was used to examine developmental trajectories of vocalization and gaze coordination. Results indicated that dyadic coordination of the timing of vocalization and gaze behaviors is a very early emerging phenomenon that is supported by both mothers and infants. Vocal coordination did not show developmental change over time, whereas mothers and infants became increasingly coordinated in their gaze behaviors as infants got older. Taken together, findings from this study highlight the importance of considering bidirectional and developmental influences on parent and infant behavior.