Electronic cigarettes (EC) are battery-powered nicotine delivery systems that have increased in popularity since they entered the US market. EC has been reported to contain less carcinogens than traditional cigarettes, cause less acute lung effects in healthy individuals, and may help with smoking cessation. It has also been viewed as a potential safer alternative for asthmatic smokers, but its effects on lung functions are unclear. However, EC do carry some harmful aspects as they contain formaldehyde and formaldehyde-forming hemiacetals as well as potentially toxic particulate matter that deposits on surfaces. EC are an increasingly popular device that could serve as a gateway into traditional cigarette smoking or illicit drugs. The popularity of EC has brought with it money from large tobacco corporations and mass marketing. Lack of regulation has generated product inconsistency and potential health hazards. This review highlights what is known and what still needs to be answered about EC.