The authors report the results of 2 studies conducted to measure the cognitive structures underlying perceived competitive relationships among retailing firms in a small city. Drawing from recent research on cognitive categorization, they first discuss the theoretical importance of studying subjective rivalry and then explain how categorization processes influence perceived competitive boundaries among firms. The results of Study 1 suggest that cognitive categories of firms are perceived to be largely independent sets of organizations. The results of Study 2 suggest that middle-level categories represent a psychological inflection point differentiating rivals from nonrivals. The authors discuss the implications of these data for studying how managers make sense of competitive structures.