For purposes of this article, the term "foreigners" means asylum seekers, resettlers, and migrant or guest workers. The article does not include data from official sources because these data are recorded only on an aggregated monthly level and would have been too broad for the purposes of this study, and because official sources were extremely uncooperative in making data available. The data source is the Chronology of Anti-Foreigner Attacks and Racist and Right-Wing Terrorism in Germany, a 2 1/2-year record of attacks on a daily basis compiled from newspaper articles by the Party of Democratic Socialism/Left List, 1993-1994. The data are not restricted to events prosecuted by the criminal justice system. More than 90 percent of the attacks on foreigners were perpetrated more or less spontaneously by groups; 72 percent of the offenders were between 15 and 20 years old; and, in one attack, more than 80 percent of the adolescents accused of offenses had consumed alcohol. The article examines internal and external incentives for violence, describes a threshold model of collective violence, and discusses costs and benefits of actions against foreigners. Figures, notes, table, bibliography