We draw from cognitive science literature on rule-based processing to develop and test a model of entrepreneurial opportunity evaluation. We argue that entrepreneurs make use of socially constructed rules as they move from the belief that an opportunity exists for someone, in general, to discern the attractiveness of an opportunity, for them, specifically. We test our model using conjoint data of 498 decisions made by 62 entrepreneurs. We find entrepreneurs’ use of rules regarding opportunity novelty, resource efficiency, and worst-case scenario significantly influences entrepreneurs’ evaluations of opportunities and differences in opportunity market and technology knowledge augment these effects. Further, we find that the worst-case scenario diminishes the positive effect of other opportunity characteristics (novelty, resource efficiency) on opportunity evaluation but that market and technology knowledge mitigates the negative effects of the worstcase scenario.