The individual difference approaches make the assumption that people’s behavior in group settings is essentially similar to their behavior in all other situations. However, in group settings, people’s behavior is often qualitatively different. This led Tajfel to suggest during the late 1970s that it is important to distinguish between interpersonal behavior and intergroup behavior, where the former means acting as an individual with some idiosynchratic characteristics and a unique set of personal relationships with others and the latter means acting as a group member. Any social behavior falls somewhere along a continuum defined by these two extremes.

Social identity theory suggests that individuals seek to feel positively about the groups to which they belong, and part of our self-esteem is derived from our social group memberships. By favorably comparing attributes of one’s own groups with those of out-groups, this theory suggests that a person acquires both a positive sense of who he or she is and a clear understanding of how he or she should act toward in-group and out-group members.

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Sources:
Encyclopedia of Applied Psychology (Click for eBook)
Social Psychology, 12th Edition by Robert A. Baron, Nyla R. Branscombe, Donn R. Byrne, Gopa Bhardwaj (Click for eBook)