In a globalized world, establishing successful cooperation between people from different nations is becoming increasingly important. We present results from a comprehensive investigation of crosssocietal cooperation in one-shot prisoner's dilemmas involving population-representative samples from six countries and identify crucial facilitators of and obstacles to cooperation. In interactions involving mutual knowledge about only the other players' nationalities, we demonstrate that people hold strong and transnationally shared expectations (i.e., stereotypes) concerning the cooperation level of interaction partners from other countries. These expectations are the strongest determinants of participant cooperation. Paradoxically, however, they turn out to be incorrect stereotypes that even correlate negatively with reality. In addition to erroneous expectations, participants' cooperation behavior is driven by (shared) social preferences that vary according to the interaction partner's nationality. In the cross-societal context, these social preferences are influenced by differences in wealth and ingroup favoritism, as well as effects of specific country combinations but not by spatial distance between nations.M any social interactions have the structure of a social dilemma, which is characterized by the fact that mutual cooperation-that is, completely transferring one's own resources to an interaction partner (or a group account)-would lead to a socially optimal outcome in that the sum of pay-offs for all persons involved is maximized. However, irrespective of the interaction partner's behavior, each individual person would be better off by defecting: that is, transferring no resources. Thus, mutual defection is the dominant strategy that should be chosen by rational money-maximizing agents (1). Still, cooperation has been observed even in fully anonymous one-shot social dilemmas (2) in which individuals interact only once, so that any selfish incentive to cooperate strategically is excluded. Specifically, it is impossible to cooperate with the aim to later profit from a good reputation (3) or reciprocity (2).Various factors have been identified that, in combination, could explain this puzzling finding. Individuals might have social preferences in that they value the outcome of others and gain utility from the absolute pay-off of other players or lose utility from inequality in pay-offs (4-6). Additionally, individuals might have specific expectations that the other player will cooperate as well (7,8). Social preferences and expectations might thereby be driven partially by similarity and kinship, in that individuals cooperate with genetically similar others to increase biological fitness of their own genotype and expect others to do the same (9, 10).In the present study, our key goal is to investigate the determinants of cooperation between people from different nations. Specifically, cooperation-related expectations and social preferences cannot only account for cooperation behavior in general. These expectations...