Background: Smoking cessation improves morbidity and mortality among smokers who achieve long-term abstinence. Many smokers are using electronic cigarettes (e-cigarettes) to attempt to quit, despite a lack of data concerning their efficacy and safety for smoking cessation. Methods: The Evaluating the Efficacy of E-Cigarette use for Smoking Cessation (E3) trial is a multicentre randomized controlled trial (NCT02417467) with a treatment period of 12 weeks and follow-up of 52 weeks. A total of 376 participants motivated to quit smoking were enrolled at 17 Canadian centres (November 2016 to September R ESUM E Contexte : Le sevrage tabagique am eliore la morbidit e et la mortalit e chez les fumeurs qui parviennent à une abstinence à long term. De nombreux fumeurs utilisent des cigarettes electroniques (e-cigarettes) pour tenter d'arrêter de fumer, malgr e le manque de donn ees concernant leur efficacit e et leur s ecurit e pour le sevrage tabagique. M ethodes : L'essai "Evaluation l'utilisation de la cigarette Électronique (E3)" pour cesser de fumer (E3)" est un essai contrôl e randomis e multicentrique (NCT02417467) avec une p eriode de traitement de 12 semaines et un suivi de 52 semaines. Au total, 376 participants More than half of adults who smoke conventional cigarettes attempted to quit in the past year, many using the increasingly popular electronic cigarette (e-cigarette). 1 Between 2014 and 2016, North Americans who made a quit attempt were more likely to use an e-cigarette (35.3%) as a cessation tool than the nicotine patch or gum (24.5%), or an approved medication such as bupropion (Zyban) or varenicline (Champix/Chantix) (12.2%). 2 The available data from randomized controlled trials (RCTs), which varied substantially in designs and populations (Supplemental Appendix S1), suggest that nicotine ecigarettes may be modestly more efficacious for smoking cessation than conventional smoking cessation therapies. 3-6 However, many of these RCTs were limited by small sample sizes, conducted in smokers not motivated to quit, or were otherwise not designed to evaluate the efficacy of e-cigarettes compared with conventional therapies. 3,5,7-11 The recent outbreak of e-cigarette, or vaping, product useassociated lung injury (EVALI) in the United States has also brought into question the safety of e-cigarettes. As of mid-January 2020, a total of 2668 people were hospitalized, and 60 had died after using e-cigarettes. 12 Mounting evidence suggests that the outbreak is likely due to the use of e-cigarette liquids containing cannabis derivatives. 13 Although most commercially available e-cigarettes are therefore unlikely to cause EVALI, additional data are required concerning their safety. The Evaluating the Efficacy of E-Cigarette use for Smoking Cessation (E3) trial will improve our understanding of the efficacy and safety of e-cigarettes for smoking cessation in North America. Methods Study design The E3 trial (clinicaltrials.gov registration NCT02417467) is a multicentre, three-arm RCT with a treatment period of 12 CJC...