Peer pressure is the direct or indirect influence on peers, i.e., members of social groups with similar interests, experiences, or social statuses. Members of a peer group are more likely to influence a person's beliefs, values, and behavior. A group or individual may be encouraged and want to follow their peers by changing their attitudes, values or behaviors to conform to those of the influencing group or individual. For the individual affected by peer pressure, this can have both a positive or negative influence on them.

Social groups include both membership groups in which individuals hold "formal" membership (e.g. political parties, trade unions, schools) and cliques in which membership is less clearly defined. However, a person does not need to be a member or be seeking membership of a group to be affected by peer pressure. An individual can be in a crowd, a group of many cliques, and still be affected by peer pressure. Research suggests that organizations as well as individuals are susceptible to peer pressure. For example, an organization may base a decision off of the current trends to receive more likeability or grow a following.

Peer pressure can affect individuals of all ethnicities, genders and ages. Researchers have frequently studied the effects of peer pressure on children and on adolescents, and in popular discourse the term "peer pressure" is used most often with reference to those age-groups. It's important to understand that for children of adolescent age, they are faced with finding their identity. Erikson, a sociopsychologist, explains that identity is faced with role confusion, in other words, these children are trying to find a sense of belonging and are the most susceptible to peer pressure as a form of acceptance. For children, the themes most commonly studied are their abilities for independent decision-making. For adolescents, peer pressure's relationships to sexual intercourse and substance abuse have been significantly researched. Peer pressure can be experienced through both face-to-face interaction and through digital interaction. Social media offers opportunities for adolescents and adults alike to instill and/or experience pressure every day.

Studies of social networks examine connections between members of social groups, including their use of social media, to better understand mechanisms such as information sharing and peer sanctioning. Sanctions can range from subtle glances that suggest disapproval, to threats and physical violence. Peer sanctioning may enhance either positive or negative behaviors. Whether peer sanctioning will have an effect depends strongly on members' expectations and the possible sanctions actually being applied. It can also depend on a person's position in a social network. Those who are more central in a social network seem more likely to be cooperative, perhaps as a result of how networks form. However, this goes both ways and so they are also more likely to participate in negative behaviors. This may be caused by the repeated social pressures they experience in their networks.