This chapter focuses on social exclusion among children and adolescents. Social exclusion has been observed among animals in their natural environment, as well as among humans in different contexts, such as the workplace and the school (Crick and Grotpeter 1995; Leung, Wu, Chen and Young 2011; McGuire and Raleigh 1986). It can be considered a serious risk factor for developing physiological, emotional, behavioral, and social problems, in particular for those youths who are repeatedly excluded and socially isolated (Sijtsema, Shoulberg and Murray-Close 2011). In this respect, depression, loneliness, and anxiety have been described as consequences of exclusion (Leary 1990). Despite much attention has been paid to the negative consequences of social exclusion, less consideration has been given to the social and moral mechanisms underlining inclusionary and exclusionary processes in the peer group. According to empirical findings, children and adolescents can legitimate social exclusion, since it allows the group to work well. For instance, youths consider legitimate to exclude incompetent peers and include skillful peers in the group, due to individual merits (e.g., ability to play baseball) (Killen and Stangor 2001). They may also interpret fairness and unfairness of social exclusion on the basis of moral judgments (e.g., rights, equal treatment, equal access to the group) or on stereotypical and contextual characteristics (e.g., gender-related group activities) (Bennett 2014; Killen 2007; Killen and Stangor 2001). In this way, social exclusion contributes to delineate social status membership and dominance positions in the peer group (Underwood and Ehnrenreich 2014). In conclusion, the present contribution aims at summarizing recent findings and theories about social exclusion, also underlining the need for intervention programs aimed at contrasting this phenomenon among youths.