Peer rejection refers to being actively disliked by one’s peers. Youth (children and adolescents) who experience peer rejection are disliked by many peers and liked by few peers, if any. Such youth often lack friends and experience peer victimization. Youth with intellectual and developmental disorders, aggressive youth, and those who are perceived to be “different” are at increased risk for experiencing peer rejection, which in turn is associated with high levels of emotional distress and negative adjustment and academic outcomes. This entry discusses the key causes and consequences of peer rejection, developmental trajectories of rejected youth, methods for assessing peer rejection, and clinical interventions for rejected youth.