‘What is an e-cigarette?’ This ostensibly simple question is central to the classification and regulation of these popular and contested devices. From their first development, e-cigarettes, which deliver nicotine via vaporisation of a liquid solution, were marketed and presented as like conventional cigarettes in crucial ways. Not only were they called electronic cigarettes, that is, a type of cigarette, but early models were designed to look like conventional cigarettes, including a tip which lit up when inhaled (Ozga et al., 2022). Moreover, the clouds of vapour they produced resembled smoke. Public health and tobacco control organisations quickly identified e-cigarettes as a threat to individual and population health. They emphasised the devices’ capacity to produce nicotine addiction (just like cigarettes), to undermine the denormalisation of smoking and to enable tobacco industry expansion (Bell & Keane, 2012; Berridge et al., 2023). The rapid rise of e-cigarette use (or vaping as it is now known) among young people has solidified and intensified this emphasis on harm. In contrast, supporters of their harm reduction potential highlight the fundamental difference of e-cigarettes from cigarettes: there is no combustion of tobacco involved in their use.