Imitation of actions is widespread in the animal kingdom, but the mental capacities thereby implied vary greatly according to the adaptive function of copying. Behavioral synchrony in social species has many possible benefits, including minimizing predation risk and using food resources optimally, but can be understood by the simple cognitive mechanism of response facilitation by priming. Imitation can send a social message, either one of short-term meshing or group identity. Where the imitative match is opaque, as in neonatal imitation, the correspondence problem may imply an innate system of behavior matching; but in other cases, no more than priming may be involved, although there are persistent suggestions that great ape imitation implies empathic abilities. Imitation in the service of learning new skills by following another's example can be divided into contextual imitation (when to employ a familiar action, and to what problem) and production imitation (learning of new skills by imitation). Cognitively, the former requires little more than response facilitation, whereas production imitation needs at least the ability to extract the statistical regularities of repeated action and to incorporate the result into hierarchical program construction. Among our close relatives, only the great apes show much evidence of production imitation of actions, along with the ability to selectively imitate the most rational components of what they observe. Copyright © 2010 John Wiley & Sons, Ltd. For further resources related to this article, please visit the WIREs website.