Theories of Status Characteristics and Expectation States use those concepts to understand the development and maintenance of power and prestige inequality structures in task groups. Expectations, roughly equivalent to ideas of task ability, emerge through interaction or from inferences based on status; once they exist they determine all features of inequality structures. These theories describe how and why that happens. They also identify ways to intervene, either to overcome inequalities or to intensify them. Applications to gender and race and to juries and sports teams illustrate the processes. This chapter presents and explains the theories and related issues in theory building, and identifies areas in which new research is extending this family of theories.