Abstract: ‘Dominance’ and ‘role’ are used in the study of human and animal social structures. It is argued here that each of these concepts is useful in two logically distinct contexts. Dominance may refer to the pattern of imbalance of interactions within a dyadic relationship in so far as that pattern is consistent between dyads, or it may refer to an aspect of group structure, namely the extent to which the individuals can be ranked in terms of who bosses whom. There is no necessary reason why these two concepts of dominance should be related. Within any group the interactions within relationships may or may not show similar patterns of imbalance, and there may or may not be an hierarchy. Role may refer to the determinants of the behaviour of incumbents of certain positions in society, or to the consequences of their behaviour on the structure of the group. Determinants and consequences of the behaviour of incumbents may be related, but are not always so. Thus, to avoid confusion in the use of each of these concepts it is essential to define precisely the manner in which it is being used.