Does scarcity of resources make us more selfish or more prosocial? This question is complex, as experimental research finds that scarcity can sometimes make us more selfish and, at other times, more prosocial. Yet, these effects are not random. In this review article, we propose a conceptual framework to organize the experimental evidence. We suggest that the impact of scarcity on prosocial behavior is mediated by situational, transient individual and social factors, and moderated by enduring individual and social factors. One particular case we explore in detail is parochialism: Does scarcity increase or decrease it? Well, it depends… In societies with tight norms, where ingroups and outgroups share similar norms, scarcity increase cooperative behavior with both groups. In contrast, in societies with loose norms, scarcity may intensify parochialism. Greater uncertainty about social norms makes cooperation riskier, prompting more ingroup favoritism. We also caution that nudges based on scarcity should be applied carefully, as they may backfire. For instance, emphasizing vaccine shortages could inadvertently lead people to prioritize others they see as more in need, ultimately reducing overall vaccination uptake. The full paper is available open access at: sciencedirect.com/science/ar… w/ @claudiacivai & @CElbaek