The 1992 Los Angeles riots, which were instigated by mob violence by the police and consisted of mob violence by citizens, have once again drawn attention to this complex phenomenon. In this chapter, we examine the instigating events, background conditions, and social and psychological processes that generate mob violence, as well as the characteristics of individuals who participate in it, with a particular focus on youth. Examples from the urban riots of the 1960s in the United States will be emphasized somewhat, partly because of the relative wealth of information about them and partly because we know that the majority of the participants in them were young people. However, we also consider other examples of mob violence, including the 1992 L.A. riots, soccer violence, prison riots, revolutionary mob violence, lynchings, and "wildings," most of which involve a substantial number of youth. Of special concern, despite limited information, are the reasons for the apparently high frequency of participation by youth in mob violence and the impact of mob violence on both participating and nonparticipating youth. Recommendations for research and for policies aimed at reducing mob violence are also made.