optimism bias, i.e. expecting the future to hold more desirable than undesirable outcomes, also extends to people that we like or admire. However, it remains unknown how the brain generates this social optimism bias. in this study, respondents estimated the likelihood of future desirable and undesirable outcomes for an in-group and three out-groups: warm-incompetent, cold-competent, and cold-incompetent. We found a strong social optimism bias for the in-group and the warm outgroup and an inverted pattern for the cold-incompetent out-group. for all groups, scores of social optimism bias correlated with the brain activity in structures that respondents differentially engaged depending on the target social group. in line with our hypotheses, evaluating the in-group recruited the ventromedial prefrontal cortex and the precuneus/posterior cingulate cortex, whereas evaluating the warm out-group engaged the posterior insula, mid cingulate cortex, and somatosensory cortices. these findings suggest different underlying cognitive mechanisms of social optimism bias for these groups, despite similar behavioural patterns. thinking about the cold out-groups recruited the right anterior temporal lobe, and temporoparietal junction. evaluating the cold-incompetent out-group additionally recruited the anterior insula, inferior frontal cortex and dorsomedial frontal cortex. We discuss these neuroimaging findings with respect to their putative cognitive functions. Human minds are highly capable of solving problems at hand, anticipating prospective issues and benefits, and planning accordingly. At the core of these skills lies the capacity to gauge the likelihood of future events 1-3. The way we assess the likelihood of future events in the general population is different from how we assess it for ourselves 4-6 , for those close to us 7-10 , and for in-group 11,12 and out-group members 11-19. Through various motivational 20,21 and cognitive mechanisms 22,23 , we manifest an optimism bias whenever we think about our future and the future of those close to us 4,8,10,11,13 but not of acquaintances or dissimilar others 8,11,14,24,25. Specifically, we expect that the future holds significantly more desirable than undesirable outcomes for ourselves and those we identify with 26. Despite a modest body of behavioural research on social optimism bias, i.e. optimism manifested towards people that we like and feel close to, very little is known about how the brain gives rise to this phenomenon 18. The primary focus of the current study was to investigate the neural correlates of group membership-driven optimism biases. To pursue this research aim and inform our hypotheses, we considered the neuroimaging literature on person perception and social cognition. A hallmark of social cognition is that individuals think differently about in-group and out-group members 27-32. Although what determines in-group and out-group membership is flexible and highly contextual 30,33 , people perceive in-group and out-group members as part of different entities wi...