The concept of dominance is used in the behavioral and biological sciences to describe outcomes in a variety of competitive interactions. In some taxa, a history of agonistic encounters among individuals modifies the course of future agonistic encounters such that the existence of a certain type of relationship can be inferred. If one is to characterize such relationships as dominance, however, then they must be distinguished from other kinds of interaction patterns for which the term tends to be used, as (...) well as from factors such as territoriality and "trained" winners and losers, which may also influence the expression of agonistic behavior. Operational definitions based on causal, functional, evolutionary, and ontogenetic considerations have been proposed. Reliability and validity problems have been discussed, but the dominance concept has proved useful despite methodological difficulties. The confusion of dominance relationships (which involve two or more individuals) with dominance ranks (which are assigned to a single individual) has obscured the possible evolutionary basis of dominance relationships. If benefits accrue to dominant members of pairs, then those attributes which allow an animal to establish dominance can be selected. Dominance per se and dominance ranks, on the other hand, cannot be genetically transmitted since they constitute relationships with other individuals rather than absolute attributes. Dominance rankings in particular may be useful for describing behavioral patterns within a group, but they may reflect our own ability to count rather than any important variable in social organization. (shrink)