This article investigates the in-flight marketplace, using detailed data of in-flight purchases to understand social effects in purchase behavior and determine their potential for designing marketing promotions. On average, a passenger is approximately 30% more likely to buy an item after being exposed to a lateral purchase. Analyses on the underlying mechanisms reveal that the classical social influence theories do not suffice to explain all the patterns in the data. The author proposes omission neglect, product contagion, and goal balancing as complementary theories. Finally, consumers’ willingness to buy is shown to be positively correlated with responsiveness to social influence. This finding indicates that homophily and social feedback effects—classically viewed in the literature as nuisances—can provide targeting value for the firm. By taking these factors into account during behavior-based targeting, firms can double the social spillovers of marketing actions.