and ethnic entrepreneurs, and generates a set of results on norm formation and change, a number of which are not intuitive. These findings suggest that (1) norms are not equally likely to form in groups with similar aggregate preference; (2) a violence-promoting norm can emerge in a group dominated by moderates, and violence is not the inevitable outcome in a group dominated by extremists; (3) strong punishments are a prerequisite for the emergence of norms that promote interethnic violence or cooperation; (4) interaction patterns matter – for example, the segregation of an ethnic group clearly inhibits norm formation; and (5) an ethnic entrepreneur can effectively amplify norm formation within a group in the absence of strong punishment.