For collective action to evolve and be maintained by selection, the mind must be equipped with mechanisms designed to identify free riders—individuals who do not contribute to a collective project but still benefit from it. Once identified, free riders must be either punished or excluded from future collective actions. But what criteria does the mind use to categorize someone as a free rider? An evolutionary analysis suggests that failure to contribute is not sufficient. Failure to contribute can occur by intention or accident, but the adaptive threat is posed by those who are motivated to benefit themselves at the expense of cooperators. In 6 experiments, we show that only individuals with exploitive intentions were categorized as free riders, even when holding their actual level of contribution constant (Studies 1 and 2). In contrast to an evolutionary model, rational choice and reinforcement theory suggest that different contribution levels (leading to different payoffs for their cooperative partners) should be key. When intentions were held constant, however, differences in contribution level were not used to categorize individuals as free riders, although some categorization occurred along a competence dimension (Study 3). Free rider categorization was not due to general tendencies to categorize (Study 4) or to mechanisms that track a broader class of intentional moral violations (Studies 5A and 5B). The results reveal the operation of an evolved concept with features tailored for solving the collective action problems faced by ancestral hunter-gatherers.