The development of self-recognition has been studied mainly by examining infants' responses to their reflections in mirrors. The definitive test is whether or not the infant is capable of using the reflection to notice and respond to a mark on the face or head by touching the mark. The mark should be inconspicuous to the infant not looking in a mirror. In general, studies agree that this response appears in some infants around 15 months of age and is shown by a majority of infants by 24 months of age. There is less agreement over the existence of a "withdrawal" component in the second year, or the presence of a "social" phase analogous to the reaction of many animals confronted with a mirror. Infants as young as 3 months are differentially responsive to a self-reflection and a live peer. Various "self-conscious" reactions and self-labelling may also indicate self-recognition in the second year, but their validity is not well established. Studies using videotapes of the self and others show that contingency of movement is a salient cue which is learned early, and that attempts to engage in contingent play and to imitate representations of oneself are useful measures of early self-recognition. The validity of the response of turning to look at an object first seen in a mirror as a sign of self-recognition is questioned. The age at which self-recognition in still pictures first appears is less clear. Verbal comprehension of self-relevant labels appears earlier than active self-labelling. A few studies have addressed the question of cognitive correlates of self-recognition, but a variety of behaviors that imply self-awareness and the corresponding ability to impute mental states to others remains to be studied in relation to self-recognition. Continued research into self-recognition and associated abilities in nonhuman primates enhances the overall understanding of the development of self-awareness.