Electronic cigarettes (e-cigarettes) have recently gained significant attention in the marketplace and in the media. However, limited information is available about the worldwide impact of e-cigarettes; most public health officials are calling for more data so they can more fully understand the potential risks and benefits of e-cigarettes in order to inform regulatory action. In the USA, e-cigarettes that are marketed as tobacco products are not currently regulated by the Food and Drug Administration (FDA). However, having a continuum of nicotine-containing products that cross jurisdictional lines within the FDA in the future would create the potential (and the need) for a comprehensive nicotine strategy at the FDA. As part of developing the most appropriate approach to e-cigarette regulation, FDA Center for Tobacco Products scientists have been reviewing the available literature to determine the state of e-cigarette knowledge and have identified research areas that could be addressed. This supplement provides a summary of the current knowledge and research gaps pertaining to e-cigarettes with regards to product design, chemistry and toxicology of e-liquid and aerosol constituents, human factor-based risk factors, abuse liability, clinical pharmacology and human health effects, paediatric issues, and environmental issues.