An electronic cigarette (e-cigarette) or vape is a device that simulates tobacco smoking. It consists of an atomizer, a power source such as a battery, and a container such as a cartridge or tank. Instead of smoke, the user inhales vapor, often called "vaping".

The atomizer is a heating element that vaporizes a liquid solution called e-liquid that cools into an aerosol of tiny droplets, vapor and air. The vapor mainly comprises propylene glycol and/or glycerin, usually with nicotine and flavoring. Its exact composition varies, and depends on matters such as user behavior. E-cigarettes are activated by taking a puff or pressing a button. Some look like traditional cigarettes, and most kinds are reusable.

Vaping is less harmful than smoking, but still has health risks. Vaping affects asthma. Limited evidence indicates that e-cigarettes are less addictive than smoking, with slower nicotine absorption rates.

E-cigarettes containing nicotine are more effective than nicotine replacement therapy (NRT) for smoking cessation, but have not been tested as rigorously as nicotine replacement therapy products.