In-Group Phenomena

The term "in-group phenomena" was made popular by Henri Tajfel and some of his colleagues while they were formulating social identity theory. An in group can, surprisingly, form quite quickly based on the interests and preferences of the persons involved.

For example, cliques (in groups) form quickly and easily in high school: athletes, fashionistas, intellectuals, etc. For adults, in-groups often revolve around politics, religion, or cultural groups but can also include civic-minded organizations (such as Rotary Club).