We conduct an international field study in which C-suite executives identify corporate peers that externalize large or small proportions of their costs. Using these evaluations, we construct a novel measure of corporate externalities based on executives’ perceptions. We first validate the measure, showing agreement among independent respondents, modest correlations with measures of specific environmental and social externalities, and predictive power for out-of-sample regulatory penalties. We then use the measure to speak to three open questions. First, we show that private companies score well, contrary to concerns that externalities are pushed out of public markets. Second, companies that score poorly have higher trailing and forward returns than companies that score well, even incremental to the carbon premium. Third, firms disproportionately include peers that score poorly in their compensation peer groups, suggesting some consideration of externalities in peer group selection. Overall, our study contributes initial evidence on a complementary approach for measuring and attributing corporate externalities.