Do economics students behave more selfishly than other students? Experimental game studies suggest so. This article investigates whether economics students’ more selfish behavior is attributable to them being less concerned with fairness, having a different notion of fairness, or being more skeptical about other players’ behavior. Students from various disciplines played a third-party punishment game and commented on the reasons for their choices. Economics students were about equally likely to mention fairness in their comments and had a similar notion of what was fair in the game; however, they expected lower offers, made lower offers, and were less likely to pay to veto low offers. The economics students’ lower expectations mediated their decisions, suggesting that they behaved more selfishly because they expected others to make more selfish decisions.