The demand for private protection and the effect of such protective measures on the level of crime are examined. Private protection may reduce a household's expected victimization rate either by deterring some crime or by diverting crime to other households. The greater the relative importance of the latter effect, the more likely a community is to "tip" in the direction of deserting the streets at night and taking other precautions. Data on crime and protection are analyzed, but they are inadequate for a full estimation of the model. The paper concludes with a normative analysis of protection and implications for social policy. © 1978.