U.S. demand for illicit drugs creates markets for Mexican drug trafficking organizations (DTOs) and helps foster violence in Mexico. This paper examines how marijuana legalization in California might influence DTO revenues and the violence in Mexico. Key findings include: 1) Mexican DTOs' gross revenues from illegally exporting marijuana to wholesalers in the United States is likely less than $2 billion; 2) The claim that 60 percent of Mexican DTO gross drug export revenues come from marijuana should not be taken seriously; 3) If legalization only affects revenues from supplying marijuana to California, DTO drug export revenue losses would be very small, perhaps 2–4 percent; 4) The only way legalizing marijuana in California would significantly influence DTO revenues and the related violence is if California-produced marijuana is smuggled to other states at prices that outcompete current Mexican supplies. The extent of such smuggling will depend on a number of factors, including the response of the U.S. federal government. 5) If marijuana is smuggled from California to other states, it could undercut sales of Mexican marijuana in much of the U.S., cutting DTOs' marijuana export revenues by more than 65 percent and probably by 85 percent or more. In this scenario, the DTOs would lose approximately 20% of their total drug export revenues.