The spectacular increases in violent crime that began in the mid-1960s continue, and Americans are currently being murdered, robbed, and raped at historically unprecedented rates. Firearms are used in a minority of violent crimes but are of special concern because more than 60 percent of the most serious crimes-criminal homicides-are committed with firearms. This essay presents a variety of evidence to the effect that the widespread availability of firearms contributes to the criminal homicide rate and influences violent crime patterns in several other respects as well. A gun is usually superior to other weapons readily available for use in violent crime; even in the hands of a weak and unskilled assailant, a gun poses a credible threat and can be used to kill quickly, from a distance, and in a relatively “impersonal” fashion. Guns are particularly valuable against relatively invulnerable targets. Hence, gun availability facilitates robbery of commercial places and lethal assaults on people who would ordinarily be able to defend themselves against other weapons. Some of the patterns of gun use in violent crime can be readily interpreted in terms of relative vulnerability of different types of victims. Guns are also more dangerous than other weapons, in the sense that victims of robbery and assault are more likely to be killed if the assailant uses a gun. On the other hand, the victim is less likely to be injured in a gun robbery than in other robberies, since the gun robber usually does not feel the need to employ physical force. This analysis suggests a number of predictions concerning the effects of gun availability on the number, distribution, and seriousness of violent crimes. In principle, these predictions could be tested directly by observing the effects of changes in gun availability on statistical characterizations of violent crime patterns. Not much research of this sort has been done, in part because it is difficult to find a suitable measure for gun availability. Future research should be directed toward remedying this problem. In the meantime, it seems fair to conclude from the available evidence that the type of weapon is not an incidental aspect of violent crime, but rather has a substantial influence on the nature of the encounter and its likely consequences.