Social species create emergent organizations beyond the individual. These emergent structures evolved hand in hand with neural, hormonal, cellular, and genetic mechanisms to support them because the consequent social behaviors helped these organisms survive, reproduce, and care for offspring sufficiently long that they too reproduced. Social neuroscience seeks to specify the neural, hormonal, cellular, and genetic mechanisms underlying social behavior, and in so doing to understand the associations and influences between social and biological levels of organization. Success in the field, therefore, is not measured in terms of the contributions to social psychology per se, but rather in terms of the specification of the biological mechanisms underlying social interactions and behavior-one of the major problems for the neurosciences to address in the 21st century.