Describing and explaining the benefits and costs of sociality have occupied the attention of political, social, and economic philosophers and social, behavioral, and developmental scientists for over 400 years. The fundamental questions have been why and how it is that self-interest becomes subordinated (or not) to the interests of group comembers and why or how group norms, values, and structures change as a consequence of the actions of their constituent members and/or the embedding contexts of the group. Whereas philosophical treatments (...) emphasized broad questions about "human nature" (e.g., egoist vs. communal) and the functional attributes of the groups (e.g., task-oriented or norm-enforcing), scientific approaches have tended to be pragmatic and problem focused (e.g., What sorts of structural features characterize different kinds of groups? Do groups have a "developmental" history? To what extent do group structures create affordances and/or impose constraints on the actions and developmental trajectories of members?). Wherever the emphasis was placed and whichever questions were asked, not until the last 80+ years have transactions within children's groups been considered relevant to those questions. In the first half of the 20th century, something of an intellectual sea change appears to have occurred in the behavioral sciences, and several researchers initiated studies of children's groups. This chapter reviews studies of affiliative structures and dominance structures in preschool children's groups. (shrink)