The National Transportation Safety Board recently recommended that states establish a per se blood alcohol concentration (BAC) limit of 0.05 or lower for all drivers who are not already required to adhere to lower BAC limits in a national effort to reduce alcohol-impaired driving. There is strong evidence for adopting this recommendation. A comprehensive review of the literature on BAC limits was conducted. The research indicates that virtually all drivers are impaired regarding at least some driving performance measures at a 0.05 BAC. The risk of being involved in a crash increases significantly at 0.05 BAC and above. The relative risk of being killed in a single-vehicle crash with BACs of 0.05–0.079 is 7–21 times higher than for drivers at 0.00 BAC. Lowering the BAC limit from 0.08 to 0.05 has been a proven effective countermeasure in numerous countries around the world. Most Americans do not believe a person should drive after having two or three drinks in 2 hours. It takes at least four drinks for the average 170-pound male to exceed 0.05 BAC in 2 hours (three drinks for the 137-pound female). Most industrialized nations have established a 0.05 BAC limit or lower for driving. Progress in reducing the proportion of drivers in fatal crashes with illegal BACs has stalled over the past 15 years. Lowering the BAC limit for driving from the current 0.08 to 0.05 has substantial potential to reduce the number of people who drink and drive in the United States and get involved in fatal crashes.