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The use of e-cigarettes in adults and adolescents has increased since 2010. Most e-cigarette users are cigarette smokers. A majority of e-cigarette users perceive them to be a tool to quit or reduce smoking. E-cigarette devices consist of a cartridge containing a liquid, an atomizer (vaporization chamber with a heating element), and a battery. The user activates the atomizer, which heats the liquid and produces a vapour to inhale. Across all brands, the main components in e-cigarette liquids are propylene glycol or glycerol, in addition, nicotine and/or flavourings can be added. A variety of other compounds have also been identified. Long-term health consequences of e-cigarette use are unknown but are likely to be less than continuing to smoke conventional cigarettes. The toxicity of chronic exposure to these and other components of e-cigarettes is uncertain. The safety and efficacy of e-cigarette use for smoking cessation is unknown. Clinicians should encourage smokers seeking to quit smoking to use US Food and Drug Administration (FDA)-approved smoking cessation aids as a first choice and make sure that newer approved strategies for smoking cessation pharmacotherapy are offered. If a smoker is not willing to use these evidence-based approaches and asks about using e-cigarettes, the clinician should not discourage e-cigarette use as long as the smoker is informed about the uncertainties of the device safety and efficacy. Public health concerns regarding e-cigarettes include their potential to increase youth initiation of tobacco products and to re-normalize tobacco use in places where cigarette smoking is not acceptable. The health effects of second-hand vapour exposure are unknown. Regulation for e-cigarettes varies worldwide and is changing. electronic cigarettes, smoking, vapour.