Social comparison-the tendency to self-evaluate by comparing ourselves to others-is an important source of competitive behavior. We propose a new model that distinguishes between individual and situational factors that increase social comparison and thus lead to a range of competitive attitudes and behavior. Individual factors are those that vary from person to person: the relevance of the performance dimension, the similarity of rivals, and their relationship closeness to the individual, as well as the various individual differences variables relating to social comparison more generally. Situational factors, conversely, are those factors on the social comparison landscape that affect similarly situated individuals: proximity to a standard (i.e., near the number 1 ranking vs. far away), the number of competitors (i.e., few vs. many), social category fault lines (i.e., disputes across vs. within social categories), and more. The distinction between individual and situational factors also helps chart future directions for social comparison research and generates new vistas across psychology and related disciplines.