Focusing on imitation in the dyad, where 1 observer (0) imitates 1 model (M), this review concerns causal relations between M's behavior and O's imitation of M's behavior. First, findings are reviewed in a manner relatively independent of processes hypothesized to mediate imitation; then theoretical viewpoints about imitation are evaluated. An extension of the best available viewpoint, that of Bandura, is presented. Finally, gaps in the literature are enumerated along with suggestions for subsequent research.