Group polarization is the tendency for group interaction to enhance group members' initial inclinations. This group polarization phenomenon, which occurs both in experimental settings and in everyday situations, provides a window through which researchers can observe group influence. Experiments have confirmed two group influences: informational and normative. The information gleaned from a discussion mostly favors the initially preferred alternative, thus reinforcing support for it. This entry begins with a look at how this line of research evolved, describes a variety of examples of group polarization, and discusses two possible explanations.