A review of the literature indicates that the following factors underlie the outbreak of a riot: (1) the perception that a crisis is required to achieve aspirations, (2) the perception that legitimate channels for achieving change are blocked, (3) the rioters' hope that their actions will accomplish the desired change, (4) the possibility that large numbers can interact under conditions of reduced social control, (5) some incident that typifies grievances and complaints, (6) the formation of consensus around suggestions for action, (7) the emergence of hostile deviant acts which go unpunished, and (8) the emergence of focused hostility as a norm for the crowd. These findings suggest a police policy for removing and isolating individuals involved in the precipitating incident. This must be accomplished before the crowd has achieved substantial unity. Further, a riot may be thwarted by interrupting communication during the milling process by dividing the crowd into small units. Also, the spread and reinforcement of the crowd should be prevented by isolating it. This is aimed at limiting the feelings of power and anonymity acquired through participation in a large crowd. Being able to respond swiftly and with specific objectives to a riot threat is clearly important, but prevention tactics must be primary. This can be done through the police establishing close and continuing links with the community to nurture confidence and the public's sense that the police are acting properly and fairly in their interventions. Eleven references are listed.