Cigarette smoke is a complex mixture of chemicals, including several tobacco-specific nitrosamines (TSNA). Most TSNA are formed in tobacco during the post-harvest period, while a number are produced when a cigarette is burned. Considerable evidence supports the role of TSNA important causative factors for cancers of the lung, pancreas, esophagus, and oral cavity in people who use tobacco products. Of the known TSNA, nicotine-derived nitrosamine ketone (NNK) and N-nitrosonornicotine (NNN) are the most carcinogenic. Other TSNA include N′-nitrosoanatabine (NAT) and N-nitrosoanabasine (NAB). New tobacco products (e.g., e-cigarettes) designed to attract consumers who are concerned about the health effects of tobacco have been appearing on the market. Several studies have reported that certain TSNA have been detected in the replacement liquids and vapour of e-cigarettes, but the levels are generally considerably lower than in tobacco cigarettes. Additionally, the FDA recently announced its intention to regulate TSNA in e-cigarettes, cigar tobacco and pipe tobacco. With the rise of new technologies for reducing the use of tobacco products—such as e-cigarettes— to evaluate exposure levels to these harmful chemicals over time, researchers will be monitoring levels of TSNA in the body as a result of the use of these devices.