Daniel Stern’s pathbreaking video-based research into the intimate complexities of mother-infant interaction has had an enormous impact on psychotherapy and developmental psychology. His minute analyses of the exchanges between mothers and babies have offered empirical support and correction for many theories of development. In the complex and instinctive choreography of "conversations," including smiles, gestures, and gazing, Stern discerned patterns of both emotional harmony and emotional incongruity that illuminate children’s relationships with others in the larger world.