Prosocial behavior is a social behavior that "benefit[s] other people or society as a whole", "such as helping, sharing, donating, co-operating, and volunteering". The person may or may not intend to benefit others; the behavior's prosocial benefits are often only calculable after the fact. (Consider: Someone may intend to 'do good' but the effects may be catastrophic.) Obeying the rules and conforming to socially accepted behaviors (such as stopping at a "Stop" sign or paying for groceries) are also regarded as prosocial behaviors. These actions may be motivated by culturally influenced value systems; empathy and concern about the welfare and rights of others; egoistic or practical concerns, such as one's social status or reputation, hope for direct or indirect reciprocity, or adherence to one's perceived system of fairness; or altruism, though the existence of pure altruism is somewhat disputed, and some have argued that this falls into the philosophical rather than psychological realm of debate. Evidence suggests that prosociality is central to the well-being of social groups across a range of scales, including schools. Prosocial behavior in the classroom can have a significant impact on a student's motivation for learning and contributions to the classroom and larger community. In the workplace, prosocial behavior can have a significant impact on team psychological safety, as well as positive indirect effects on employee's helping behaviors and task performance. Empathy is a strong motive in eliciting prosocial behavior, and has deep evolutionary roots.

Prosocial behavior fosters positive traits that are beneficial for children and society. It helps many beneficial functions by bettering production of any league and its organizational scale. Evolutionary psychologists use theories such as kin-selection theory and inclusive fitness as an explanation for why prosocial behavioral tendencies are passed down generationally, according to the evolutionary fitness displayed by those who engaged in prosocial acts. Encouraging prosocial behavior may also require decreasing or eliminating undesirable social behaviors.

Although the term "prosocial behavior" is often associated with developing desirable traits in children, the literature on the topic has grown since the late 1980s to include adult behaviors as well. The term "prosocial" has grown into a world-wide movement, using evolutionary science to create real-world pro-social changes from working groups to whole cultures.

According to the psychology researcher Daniel Batson, the term "was created by social scientists as an antonym for antisocial."

The concept of prosocial behavior in psychology gained popularity in the 1970s. It was introduced to describe acts that promote positive social outcomes, such as cooperation and helping, and has since been examined through the lens of evolutionary biology, neuroscience, and cross-cultural psychology. Interest in prosocial behavior has deep historical roots, particularly within religious, philosophical, and psychological traditions.

The purest forms of prosocial behavior are motivated by altruism, an unselfish interest in helping another person. According to psychology professor John W. Santrock, the circumstances most likely to evoke altruism are empathy for an individual in need, or a close relationship between the benefactor and the recipient. However, many prosocial behaviors that appear altruistic are in fact motivated by the norm of reciprocity, which is the obligation to return a favor with a favor. People feel guilty when they do not reciprocate and they may feel angry when someone else does not reciprocate. Reciprocal altruism suggests that "such helping is driven by a genetic tendency". Thus some professionals argue that altruism may not exist, and is completely motivated by reciprocity. Either reciprocity or altruism may motivate many important prosocial behaviors, including sharing.

Prosocial behavior is mediated by both situational and individual factors.

One of the most common situation factors is the occurrence of the bystander effect. The bystander effect is the phenomenon that an individual's likelihood of helping decreases when passive bystanders are present in a critical situation. For example, when someone drops a stack of papers on a crowded sidewalk, most people are likely to continue passing him/her by. This example can be extended to even more urgent situations, such as a car crash or natural disaster. Bystanders are less likely to intervene as group size increases when surrounded by strangers, but they become more likely to help when accompanied by friends.