A critical review of the small group literature is undertaken in an attempt to identify those characteristics which distinguish the dyad, the two-person group, from larger groups. Comparisons of dyads to larger groups are made in five categories of major small group variables: influence processes, affiliation processes, role differentiation and variability, task factors, and communication patterns. Ten important empirical and conceptual distinctions are analyzed, and the major limitations in the research are noted. Three implications of the unique nature of the dyad are suggested: results of research based on large groups may not be generalized to dyads; results based on dyads may not be generalized to larger groups; and in spite of several similarities between dyads and larger groups, the distinctive features of several major dyadic components serve to distinguish the dyad as a unique communication system. (Author/RB)