This paper studies demand, fatalities, and regulation in firearm markets. I assemble 20 years of administrative data from California, recording all licit handgun purchases and fatalities. Leveraging variation from the entry timing of firearm retailers, I find that consumers are elastic in their handgun purchase and ownership decisions, and that handgun ownership causes homicides. An estimable model of handgun demand and fatalities reveals that handgun owners are adversely selected: those with higher willingness-to-pay for handguns also generate more homicides as owners. The model suggests that efficiency-improving firearm regulation could be targeted towards younger adults and/or feasibly decentralized across space.