Electronic cigarette (eCigarette, e-cigarette), also electronic inhaler or personal inhaler is an electronic device which simulates the feeling of smoking a classic tobacco cigarette, and is an alternative to classic tobacco products. Unlike the classic cigarette, the electronic cigarette does not produce smoke but rather vapour containing nicotine (if nicotine-free e-liquid is used, the vapour does not contain nicotine). Electronic cigarette heats the e-liquid, turning it into smoke-like flavoured vapour. The vapour produced by electronic cigarettes contains very few substances which are not toxic and are safe for human consumption. All substances in electronic cigarettes, apart from nicotine, are used in food and cosmetic industries.

Electronic cigarettes enable nicotine delivery in almost identical manner as tobacco cigarettes. It is often labelled (although not officially) as an aid to stop smoking or a replacement for tobacco or regular cigarettes. E-cigarette users often overcome their nicotine addiction by gradually reducing nicotine content in e-liquid and consequently giving up e-cigarettes. There are many different electronic cigarettes in the market, differing in quality, shape and mode of operation. In addition, the use of e-cigarettes is a lot less expensive than smoking cigarettes, as the long term cost of e-cigarette use is a lot lower than the cost of classic cigarettes.

First generation e-cigarettes, sometimes called cigalikes, are designed to look like a cigarette and generally use cartomisers. When the user takes a puff (or presses a button on some models) a heating coil is activated to vapourise the e-liquid, creating a vapour that can be inhaled. Many first generation models have a light on the end of the device that also glows when a puff is taken. More experienced e-cigarette users (vapers) prefer to use newer (second and third) generation e-cigarettes. Often called personal vaporisers, these are particularly popular with people who have completely replaced their cigarette smoking with e-cigarette use.

Second generation e-cigarettes are typically larger and have a more powerful battery linked to an atomiser and a ‘tank’. The user fills the tank with their choice of e-liquid which may include flavours and contain nicotine in different concentrations. These devices often look like a fountain pen and can be used with a range of atomisers, cartomisers and tank systems. They typically use larger batteries and
may have adjustable power settings.

Third generation e-cigarettes are usually larger still with a more powerful battery and adjustable air flow. They also allow the user to adjust the voltage or wattage applied to the atomiser (often referred to as ‘variable voltage’ or ‘variable wattage’ devices). Some come with ‘puff counters’ or downloadable software that allow users to program their own voltage and wattage level, and to monitor their patterns of use. Third generation devices are designed to allow modifications and substitution of individual components according to user preference.