The seminar presents my research work investigating social exclusion of people from marginalized groups. Marginalization is an extreme form of exclusion when episodes of rejection, ostracism, and isolation persist over time and are pervasive across social contexts and situations. What are the psychosocial repercussions of such extreme, chronic exclusion? How can it be prevented? The first part of the seminar describes a series of studies investigating the exclusion repercussions on migrants, homeless, and detained people. Correlational, experimental, and longitudinal evidence highlights the immediate and long-term repercussions of exclusion on forced and voluntary migrants’ emotions and psychological well-being, further showing how intergroup social connections with other migrants or native people moderate these effects. Quasi-experimental evidence underscores the exclusion impact on homeless and detained people’s well-being, emphasizing the intervening role of group-specific factors and situations. This section concludes by addressing how social exclusion intersects with social identification dynamics to shape marginalized groups’ well-being and proposing a theoretical perspective with preliminary data linking chronic exclusion to radicalization and extremism. The second part of the seminar addresses the psychosocial factors that prevent exclusionary behaviors and attitudes among dominant groups. Results based on cross-national data uncover the mechanisms linking intergroup contact with migrants to natives’ collective and individual actions to exclude or include them. Additionally, a set of studies underscores the potential of Virtual Reality protocols to fill the empathy gap toward homeless and detained people, fostering inclusive attitudes and behaviors. The seminar concludes by showing results from a novel methodology bridging GPS data with the assessment of momentary interactions to investigate the contextual effects of urban segregation on intergroup contact opportunities. The seminar sheds light on group-specific processes that influence the repercussions of extreme exclusion for marginalized groups’ well-being, identification, and radicalization, and highlights innovative pathways to prevent exclusion from dominant groups.