Although field experiments and classroom surveys are ambiguous about whether economists are less likely than others to cooperate in social dilemmas, three important points remain clear: economics training encourages the view that people are motivated primarily by self-interest; there is clear evidence that this view leads people to expect others to defect in social dilemmas; and there is also evidence that, when people expect partners to defect, they are overwhelmingly likely to defect themselves. These points' logical implications appear to place a heavy burden of proof on those who insist economics training does not inhibit cooperation.