Electronic cigarettes (e-cigarettes or electronic nicotine delivery systems) heat a nicotine solution to generate vapor that is inhaled, without the combustion of tobacco and its toxic constituents. Use of e-cigarettes is increasing in the United States and around the world. Current smokers in the United States report an 11.4% prevalence of ever use of e-cigarettes and 4.1% use in past 30 days.1 They likely pose less direct hazard to the individual smoker than tobacco cigarettes and might help smokers quit smoking or reduce harm by smoking fewer tobacco cigarettes. On the other hand, there are potential harms, including promoting continued smoking of cigarettes and renormalizing cigarette smoking behaviors. The Food and Drug Administration (FDA) is authorized to regulate tobacco products, and in 2011 the agency announced plans to regulate e-cigarettes as tobacco products.2 The FDA will need to make a number of regulatory decisions about product safety that could have major effects on public health and will face many challenges.