Much research has been carried out to understand how human brains make sense of another agent in motion. Current views based on human adult and monkey studies assume a matching process in the motor system biased toward actions performed by conspecifics and present in the observer's motor repertoire. However, little is known about the neural correlates of action cognition in early ontogeny. In this study, we examined the processes involved in the observation of full body movements in 4-month-old infants using functional near-infrared spectroscopy to measure localized brain activation. In a 2 × 2 design, infants watched human or robotic figures moving in a smooth, familiar human-like manner, or in a rigid, unfamiliar robot-like manner. We found that infant premotor cortex responded more strongly to observe robot-like motion compared with human-like motion. Contrary to current views, this suggests that the infant motor system is flexibly engaged by novel movement patterns. Moreover, temporal cortex responses indicate that infants integrate information about form and motion during action observation. The response patterns obtained in premotor and temporal cortices during action observation in these young infants are very similar to those reported for adults. These findings thus suggest that the brain processes involved in the analysis of an agent in motion in adults become functionally specialized very early in human development.