ABSTRACT: AIMS:To examine current and ex-smokers' reasons for continuing or discontinuing regular use of nicotine vaping products (NVPs). DESIGN AND PARTICIPANTS:Cross-sectional study of 2722 current daily/weekly, and 921 ex-daily/weekly, adult vapers who were either current or ex-cigarette smokers when surveyed. SETTING:2016 ITC Four Country Smoking and Vaping wave 1 (4CV1) surveys conducted in the United States (n = 1159), England (n = 1269), Canada (n = 964) and Australia (n = 251). MEASUREMENTS:Current vapers were asked about the following reasons for regular NVP use: less harmful to others, social acceptance, enjoyment, use in smoke-free areas, affordability and managing smoking behaviour. Ex-vapers were asked about the following reasons for discontinuing regular NVP use: addiction concerns, affordability, negative experiences, perceived social unacceptability, safety concerns, product dissatisfaction, inconvenience, unhelpfulness for quitting, unhelpfulness for managing cravings and not needed for smoking relapse prevention. Possible correlates of NVP use and discontinuation, including smoking status, smoking/vaping frequency, quit duration (ex-smokers only), country, age and type of NVP device used, were examined using multivariate logistic regression models. FINDINGS:For current smokers, the top three reasons for current regular NVP use were: helpful for cutting down smoking (85.6%), less harmful to others (77.9%) and helpful for quitting smoking (77.4%). The top three reasons for discontinuing vaping were: not being satisfying (77.9%), unhelpfulness for cravings (63.2%), and unhelpfulness for quitting smoking (52.4%). For ex-smokers, the top three reasons for current vaping were: enjoyment (90.6%), less harmful to others (90%) and affordability (89.5%); and for discontinuing were: not needed to stay quit (77.3%), not being satisfying (49.5%) and safety concerns (44%). Reported reasons varied by user characteristics, including age, country and NVP device type. CONCLUSIONS:Regular use of nicotine vaping products is mainly motivated by its perceived benefits, especially for reducing or quitting smoking, whereas its discontinuation is motivated by perceived lack of such benefits, with some variation by user characteristics.