The Los Angeles riot of 1992 resulted in 52 deaths, 2500 injuries and at least $446 million in property damage; this staggering toll rekindled interest in understanding the underlying causes of the widespread social phenomenon of rioting. We examine the causes of the rioting using international data, evidence from the race riots of the 1960's in the US, and Census data of Los Angeles, 1990. We find some support for the notions that the opportunity costs of time and the potential costs of punishment influence the incidence and intensity of riots. Beyond these individual costs and benefits, community structure matters. In our results, ethnic diversity seems a significant determinant of rioting, while we find little evidence that poverty in the community matters.