In the present contribution, we examine psychological features of extreme political ideologies. In what ways are political left- and right-wing extremists similar to one another, and different from moderates? For this purpose, we propose and review four interrelated propositions that explain adherence to extreme political ideologies from a psychological perspective. We specifically argue that (1) psychological distress stimulates adopting an extreme ideological outlook; (2) extreme ideologies are characterized by a relatively simplistic, black-and-white perception of the social world; (3) due to such mental simplicity, political extremists are overconfident in their judgments; and (4) political extremists are less tolerant of different groups and opinions than political moderates. In closing, we discuss how these psychological features of political extremists increase the likelihood of conflict between groups in society.