Social Identity Theory proposes that people have both a personal identity and a social identity based on their group memberships. It involves three main cognitive processes: social categorization, social identification, and social comparison. Social categorization involves dividing the social environment into in-groups that one belongs to and out-groups that one does not belong to. Social identification is adopting the identity of the in-group as part of one's self-concept. Social comparison involves comparing one's in-group to out-groups in order to enhance self-esteem.