Few topics in public health and medicine are as contentious as electronic cigarettes (e-cigarettes), novel handheld battery-operated nicotine-delivery devices that resemble conventional tobacco cigarettes and simulate the experience of smoking a cigarette.1-3 Unlike cigarettes that burn tobacco to generate smoke, e-cigarettes heat a liquid consisting of nicotine, propylene glycol or glycerin, flavorings, and other chemicals to create a vapor that is inhaled. Both conventional cigarettes and e-cigarettes deliver nicotine, the addictive agent in tobacco, but e-cigarettes do not expose the user to the many other tobacco smoke constituents responsible for causing tobacco-related diseases. e-Cigarettes therefore offer the tantalizing prospect that they could reduce the harms of conventional tobacco use, the leading cause of preventable death and disability in the United States and worldwide.4