Social Identity Theory is a psychological framework that explains how individuals categorize themselves and others into social groups. This theory suggests that people derive a sense of self from their group memberships, such as nationality, ethnicity, or religion. By identifying with a group, individuals enhance their self-esteem and create a sense of belonging, which can influence their behavior and attitudes toward others. The theory also highlights the tendency to favor one's own group, known as in-group bias, while often viewing other groups, or out-groups, less favorably. This can lead to stereotypes, discrimination, and intergroup conflict, as individuals strive to maintain a positive social identity through comparisons with others.