The discovery of mirror neurons in the monkey brain and the subsequent description of a mirror neuron system (MNS) in humans have triggered unprecedented interest in the neural basis of social cognition. Although the mechanism matching action observation and execution is now well documented in human adults, much remains to be learned about its normal development. In light of accumulating evidence suggesting a link between impaired motor resonance and developmental disorders such as autism spectrum disorder, it is of paramount importance to better understand how the MNS develops and under what specific conditions it appears. Until recently, speculation about the existence of a functioning MNS in the infant brain relied primarily on evidence of imitative behavior shortly after birth. Here, we describe studies that have tackled the issue of detailing MNS properties in the immature brain. Through a variety of neuroimaging techniques, a preliminary description of neurophysiological mechanisms underlying early imitation and action understanding is starting to emerge. We will see, however, that although important first steps have been taken, much remains to be learned about early mirroring processes and their relationship to social behavior.