A sociological framework is proposed for studying nonconformity in competitive repertoires. We argue that the extensiveness and continuity of a company's market interactions very much influence its level of nonconformity. Market-level factors that might influence nonconformity include customer and competitor diversity and the continuity of traditions; and firm-level factors include the size, resources, and industry experience of an organization. Nonconformity may also be driven by economic factors such as market growth and financial returns. Most of these sources of nonconformity were confirmed in a study of the competitive repertoires of the major U.S. airlines. The findings also show that competitive nonconformity was associated with subsequent declines in financial performance, but mainly for smaller airlines with homogeneous markets. This study supported some central notions from the sociology of markets and, with qualification, from institutional theory.