Adolescent cliques are cliques that develop amongst adolescents. In the social sciences, the word "clique" is used to describe a large group of 6 to 12 "who interact with each other more regularly and intensely than others in the same setting". Cliques are distinguished from "crowds" in that their members socially interact with one another more than the typical crowd (e.g. hang out together, go shopping, play sports etc.). Crowds, on the other hand, are defined by reputation. Although the word 'clique' or 'cliquey' is often used in day-to-day conversation to describe relational aggression or snarky, gossipy behaviors of groups of socially dominant teenage girls, that is not always accurate. Interacting with cliques is part of normative social development regardless of gender, ethnicity, or popularity. Although cliques are most commonly studied during adolescence and in educational settings, they can exist in all age groups and settings.

As children enter adolescence, cultural, biological and cognitive changes cause variation in their daily lives. Adolescents spend far less time with their parents and begin participating in both structured and unstructured peer activities. Without the direct presence of their parents or other adults, their peer network begins to become the primary context for most socialization and activity. There was an explanation given by B. Bradford Brown on the psychological development stages in adolescents, and one of the stages He named "to fit in" stage, which means to find secure affiliations and obtain approval from peers. He said that adolescents spend a lot more time with their peers than younger children, and are more influence by the peer group than younger children. These social "cliques" fundamentally influence adolescent life and development. Perhaps because they are perceived as an external threat to parental authority, undesired changes in adolescent behavior are often attributed to cliques. In these situations, cliques are described as "social grouping[s] of persons that exhibit a great deal of peer pressure on its members and is exclusive, based on superficial differences". Researchers, however, question these assumptions: based on empiric data from both experiments and ethnographies they suggest that clique structure characterizes many friendship networks within any given school, not all of which negatively affect adolescents. A more neutral and scientific definition of clique is "a grouping of persons who interact with each other more regularly and intensely than others in the same setting".

Although cliques can range from two to twelve people, cliques typically consist of five or six people who are homogeneous in age, gender, race, social status, and socioeconomic background. More subtle determinant of group membership, such as shared interests and values, take precedence as adolescents develop more sophisticated, abstract cognitive functions (more here), which allow them to categorize individuals in more subtle ways and better interpret social interactions. Consistent group identities thus allow individuals to cope with the anonymity and intimidation that often accompany the transition into large secondary schools.

Similar cliques may re-emerge in adulthood in specific contexts, characterized by large, undifferentiated, anonymous crowds. Overall, cliques are a transitory social phase. In general, cliques first form in early adolescence with strict gender segregation, but by middle adolescence, some mixed-gender activities within the peer crowds foster close, cross-sex friendships which begin to restructure the clique. During late adolescence, the organized clique structure typically dissolves into associated sets of couples, which then remain the primary social unit into and throughout adulthood.

Cliques are different from other types of peer groups often seen in the average school, which are often reputation-based groups such as jocks or nerds. The major difference is that these reputation-based groups do not necessarily interact with each other, whereas members of a clique do interact with one another and have frequent social interactions. For example, football players are considered jocks, but not all members of a football team always interact with each other.

Although the popular media portrays female cliques almost exclusively (see examples in movies, television, and young adult fiction), clique membership is almost equally prevalent in adolescent boys. Girls do, however, tend to form cliques earlier (11 years old as compared with 13 or 14 among boys), which may contribute to the greater popular salience of female cliques. Additionally, the activities central to most female cliques include gossip and emotional sharing; this behavior visibly increases, revealing female cliques to the outside observer. Male cliques, on the other hand, tend to center around activities that have occurred before the formation of the clique (common examples include sports and other shared activities or interests, such as music or reading), and thus may draw less attention to the appearance of male cliques. Male cliques may have also gone largely unnoticed because they often appear less exclusive toward the non-clique peer group members. This last difference may arise because males more frequently reported ambitions related to acceptance and status throughout their crowd, whereas females more often aspired to status and close bonds with only a few peers (i.e. a clique). Males were also more likely to consider actively exclusive behavior unethical, as were younger adolescents. The stereotype of cruel, unwelcoming clique members is well supported in some cases, but other cliques are more open to drifters. Both attitudes appear in some cliques of both sexes and all social groups become more permeable with age. Similarly, although adolescents tend to associate with others of the same ethnicity and socioeconomic status, clique membership is equally common across ethnicity and economic background. The characteristics of the distinct cliques within each demographic group also vary equally, although members of cliques in one crowd or demographic group may not perceive all of the distinctions in others (see also crowds).

A number of recent studies confirm that regardless of gender, ethnicity, or socioeconomic status, adolescents tend to fall into one of three categories: group members, liaisons, and isolates.

Membership type is far more stable over time than membership in an individual clique: isolates generally remain socially disengaged, liaisons remain equally consistent, and "group members" frequently switch from one clique to another, but typically remain group members over time. The objective cliques themselves remain surprisingly stable as well. On average, cliques lose around one third of their members over a given school year, but new members with similar characteristics tend to replace the deserters, maintaining the general identity of the clique. Clique membership becomes more stable across time, as well as more permeable, less exclusive, and less hierarchical. Contrary to popular belief, individual friendships are far less stable across the school year. This is particularly true of high-status cliques and individuals, in which clique members must critically analyse their friendships and socialize only with their most popular peers or risk losing membership and status.