An electronic cigarette, or e-cigarette, is an electrical device that simulates 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; though without its odor, and intended to omit its health risks. 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.

Most electronic cigarettes are portable, self-contained cylindrical devices the size of a ballpoint pen or magic marker; though sizes vary, mainly due to differing battery capacities. Many electronic cigarettes are designed to resemble actual cigarettes or cigars, or even pipes. Most are also reusable, with replaceable and refillable parts, but some models are disposable.

The primary stated use of the electronic cigarette is an alternative to tobacco smoking, or 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.