An electronic cigarette, or e-cigarette, is an electrical device that attempts to simulate the act of tobacco smoking by producing an inhaled mist bearing the physical sensation, appearance, and often the flavor and nicotine content of inhaled tobacco smoke. The device uses heat, or in some cases ultrasonics, to vaporize a propylene glycol- or glycerin-based liquid solution into an aerosol mist, similar to the way a nebulizer or humidifier vaporizes solutions for inhalation. Nicotine, if present in the liquid solution being used, is absorbed through membranes of the mouth and lungs.

The primary stated use of the electronic cigarette is as a smoking cessation device, as it attempts to deliver the experience of smoking without, or with greatly reduced, adverse health effects usually associated with tobacco smoke. Nevertheless, concerns have been raised that use of the device still carries health risks, and that it could appeal to non-smokers, especially children, due to its noveltyflavorings, and possibly overstated claims of safety.

The possible benefits or adverse effects of electronic cigarette use are a subject of disagreement among different health organizations and researchers. Controlled studies of electronic cigarettes are scarce due to their relatively recent invention and subsequent rapid growth in popularity. Laws governing the use and sale of electronic cigarettes, as well as the accompanying liquid solutions, currently vary widely, with pending legislation and ongoing debate in many regions.

Most electronic cigarettes are designed to resemble actual tobacco smoking implements, such as cigarettes, cigars, or pipes, but many take the form of ballpoint pens or screwdrivers since those designs are more practical to house the mechanisms involved. Most are also reusable, with replaceable and refillable parts, but some models are disposable.

The electronic cigarette was invented by Chinese pharmacist Hon Lik in 2003 and introduced to the market the following year. The company he worked for, Golden Dragon Holdings, changed its name to Ruyan (meaning "to resemble smoking"), and started exporting its products in 2005–2006.