The purpose of this paper is to illustrate and explain the role bystanders play in crime control. We describe the range of bystanders' reactions to crime including nonintervention, indirect intervention, direct intervention, and spontaneous vigilantism, and cite illustrations of each from mass media accounts. Using evidence from social psychological research, we discuss conditions under which each type of reaction would be expected to occur. Evidence is then presented that the mere presence of bystanders capable of surveillance may inhibit the commission of crime. A cyclical model is then discussed in which fear of crime reduces the number of bystanders available for surveillance, decreasing the risks of crime and potentially increasing its occurrence. This model suggests that under certain circumstances crime causes crime and implies that an important factor in the social control of crime is the relative balance between the offender's fear of surveillance and the bystander's fear of crime.