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An electronic cigarette is an electronic 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. As such, using an e-cigarette is often called “vaping”.The atomizer is a heating element that vaporizes a liquid solution called e-liquid, which quickly cools into an aerosol of tiny droplets, vapor, and air. E-cigarettes are activated by taking a puff or pressing a button. Some look like traditional cigarettes, and most versions are reusable.

Vaping is likely significantly less harmful than smoking tobacco, although it nevertheless carries health risks. The life expectancy of tobacco smokers is at least 10 years shorter than for nonsmokers. E-cigarette vapor contains fewer toxins, in lower amounts than cigarette smoke. Nicotine is addictive, but by itself is not greatly harmful. For people trying to quit smoking with medical help, e-cigarettes have a higher quit rate than normal nicotine replacement therapy.

An electronic cigarette consists of an atomizer, a power source such as a battery, and a container for the e-liquid such as a cartridge or tank. E-cigarettes have evolved over time, and the different designs are classified in generations. First-generation e-cigarettes, which tend to look like traditional cigarettes, are called “cigalikes”. Second-generation devices are larger and look less like traditional cigarettes. Third-generation devices include mechanical mods and variable voltage devices. The fourth generation includes sub-ohm tanks (meaning that they have an electrical resistance of less than 1 ohm) and temperature control devices. There are also pod mod devices that use protonated nicotine, rather than free-base nicotine found in earlier generations, providing higher nicotine yields through the production of aerosolized protonated nicotine.

The mixture used in vapor products such as e-cigarettes is called e-liquid. E-liquid formulations vary widely. A typical e-liquid comprises propylene glycol and glycerin (95%), flavorings, nicotine, and other additives (5%). The flavorings may be natural, artificial, or organic. Over 80 chemicals such as formaldehyde and metallic nanoparticles have been found in the e-liquid. There are many e-liquid manufacturers, and more than 15,000 flavors. In the US, under Food and Drug Administration (FDA) rules, e-liquids must comply with manufacturing standards. Industry standards are published by the American E-liquid Manufacturing Standards Association (AEMSA).

Since their entrance to the market around 2003, e-cigarette use has risen rapidly. In 2011 there were about 7 million adult e-cigarette users globally, rising to 68 million in 2020 compared with 1.1 billion cigarette smokers. There was a further rise to 82 million in 2021. The rise was thought to be due to targeted marketing, their lower cost than cigarettes, and the fact that e-cigarettes are safer than tobacco. E-cigarette use is highest in China, the US, and Europe, with China having the most e-cigarette users.

It is commonly stated that the modern e-cigarette was invented in 2003 by Chinese pharmacist Hon Lik, but tobacco companies had been developing nicotine aerosol generation devices since as early as 1963.