This article reviews the results of experimental studies on imitative behavior reported by various investigators, and then discusses the possible brain mechanisms responsible for this behavior. It was found that human infants in their first hours of life were already capable of spontaneous imitation of simple motor acts demonstrated by an adult, without previous training or reward; these observations suggest that imitative behavior is an innate process that can be considered an unconditional reflex of imitation. It was also found that satiated animals resumed eating when they saw their companions eating. In the latter case, the imitative reflex triggered the previously acquired feeding behavior. Similar mechanisms could be responsible for the phenomenon of eating more in the presence of companions than in their absence, as well as that of preferring the food chosen by companions. When followed by a reward, the imitative act can be learned--that is, transformed into an instrumental conditional response; learning by imitation of simple motor acts was observed in animals, and that of complex motor acts was observed in children who had already achieved a certain developmental stage. In animals, learning complex motor tasks was facilitated by previous observation of a companion performing this task. In this case, the presence of the observer during the session could lead to habituation of the experimental situation and production of associations between this situation and stimuli or emotions related to the reward or punishment, and might result in more efficient learning later. The imitative behavior can be inhibited by stimuli producing responses antagonistic to the act of imitation.