There are two major components in explaining the crime drop in the United States in the 1990s. First, is the undoing of the rise in violence by young people with handguns between 1985 and 1993. Second, was the general continuation of the crime drop by people over 30 that had begun before 1980. The drop by the young people was significant and has consumed much of the attention. The crime decline of the 1990s largely came to an end by 2000. The period between 2000 and 2005 saw no significant change in aggregate violence rates. One issue that has attracted considerable attention in the United States and around the world has been the impressive decline in violent crime in the United States from about 1993 to 2000. In particular, murder and robbery rates both declined over 40 percent during that period. There has been a widespread search for explanations of this trend. This study examined the data on the crime decline and a variety of explanations that have been proposed. The focus is on murder and robbery because they are both well defined crimes and are well measured in police reports. The study examined the effects of incarceration, changing demographics, policing and control of guns, and the changing nature of markets selling crack cocaine. Figures, references