Abstract: The "chameleon effect" refers to the tendency to adopt the postures, gestures, and mannerisms of interaction partners (Chartrand & Bargh, 1999). This type of mimicry occurs outside of conscious awareness, and without any intent to mimic or imitate. Empirical evidence suggests a bi-directional relationship between nonconscious mimicry on the one hand, and liking, rapport, and affiliation on the other. That is, nonconscious mimicry creates affiliation, and affiliation can be expressed through nonconscious mimicry. We argue that mimicry played an important role in human evolution. Initially, mimicry may have had survival value by helping humans communicate. We propose that the purpose of mimicry has now evolved to serve a social function. Nonconscious behavioral mimicry increases affiliation, which serves to foster relationships with others. We review current research in light of this proposed framework and suggest future areas of research. (PsycINFO Database Record (c) 2005 APA, all rights reserved) (journal abstract).