Adopting a functionalist perspective, we emphasize the interest of considering imitation as a single capacity with two functions: communication and learning. These two functions both imply such capacities as detection of novelty, attraction toward moving stimuli and perception-action coupling. We propose that the main difference between the processes involved in the two functions is that, in the case of learning, the dynamics is internal to the system constituted by an individual whereas in the case of communication, the dynamics concerns the system composed by the perception of one individual coupled with the action of the other. In this paper, we compare the first developmental steps of imitation in three populations: typically developing children, children with autism, and robots.