This article reviews the most commonly cited, representative, empirical studies in the peer-reviewed literature that directly investigate the association of gun availability and homicide victimization. Individual-level studies (n=4) are reviewed that investigate the risks and benefits of owning a personal or household firearm. The research suggests that households with firearms are at higher risk for homicide, and there is no net beneficial effect of firearm ownership. No longitudinal cohort study seems to have investigated the association between a gun in the home and homicide. Two groups of ecological studies are reviewed, those comparing multiple countries and those focused solely on the United States. Results from the cross-sectional international studies (n=7) typically show that in high-income countries with more firearms, both men and women are at higher risk for homicide, particularly firearm homicide. Time series (n=10) and cross-sectional studies (n=9) of U.S. cities, states, and regions and for the United States as a whole, generally find a statistically significant gun prevalence–homicide association. None of the studies prove causation, but the available evidence is consistent with the hypothesis that increased gun prevalence increases the homicide rate.