Group polarization is a phenomenon studied in the social sciences in which the decisions and opinions of individuals become more extreme when they are in group settings. According to the idea of group polarization, if an individual holds an opinion about a topic, that opinion will likely be enhanced after a discussion on the topic with a group. In many cases, the concept of "more extreme decisions" is interpreted to strictly refer to riskier, wilder decisions. It is important to note that the decisions and actions in a group may tend toward either extreme or pole, and can either be more cautious or more risky than a decision made by an individual.

There are several theories about the origin of group polarization, but the precise cause, if there is actually a single well-defined case, is not known. One theory revolves around the idea of social comparison, the idea that all members of a group are constantly analyzing the behavior of others and attempting to act in a socially advantageous way. This often involves acting in a way that is somehow superior to the perceived "average" general behavior or stance on a topic. In many cases, this means taking a more extreme stance on an issue. Assuming that everyone in the group is consciously or subconsciously working for social advantage in the group, the overall opinion of the group tends to shift to a more extreme stance.

Another possible explanation for the phenomenon of group polarization is based simply on commitment. By taking any stance at all on a topic in a group, one must maintain that stance to avoid seeming unsure or indecisive. Additionally, turning a vague inclination toward one side of an issue or another into a statement made in front of a group turns the inclination into a concrete opinion with witnesses. Moderate opinions or slight inclinations become much more real when put into words and heard by other people. When members of a group state an opinion or commit to a course of action, the rest of the groups expects them to stick to it.

It has been observed that group polarization occurs in online discussions as well as in physical discussions. This is especially true when those taking part in the discussion are anonymous. There tends to be a factor of "one-upmanship" in such discussion as people attempt to voice more shocking, original, and noteworthy opinions and ideas. This results in an overall group polarization effect as ever-more-extreme opinions and ideas are introduced to the discussion.