We aimed to examine prevalence and correlates of past-month electronic cigarette ("e-cigarette") use and use of e-cigarettes to aid a cessation attempt in three samples of young adult smokers recruited online in 2009-2010 (Study 1), 2010-2011 (Study 2), and 2013 (Study 3).Participants were young adults aged 18 to 25 who smoked at least one cigarette in the previous month (Study 1, N=1987 and Study 2, N=570) or smoked 3 or more days each week and used Facebook 4 or more days per week (Study 3, N=79). We examined both past-month e-cigarette use and ever use of e-cigarettes to quit conventional cigarettes.Prevalence of past-month use of e-cigarettes was higher in each subsequent study: Study 1 (6%), Study 2 (19%), and Study 3 (41%). In multivariate analyses, significant correlates of past-month e-cigarette use were identified for Study 1 (male sex OR=2.1, p=.03; past-year quit attempt OR=1.6, p=.03) and Study 2 (male sex, OR=1.7, p=.03; younger age OR=0.88, p=.05), but not Study 3. In multivariate analyses, significant correlates of ever use of e-cigarette to quit conventional cigarettes were identified for Study 1 (education, OR=1.2, p=.02; smoking within 30min of waking, OR=2.8, p=.02; past year quit attempt OR=4.1, p=.02), and Study 3 (desire to quit smoking, OR=1.3, p=.02), but not Study 2.E-cigarette use is increasingly common among young adults, particularly men. E-cigarette use for quitting conventional cigarettes appears more common among those more nicotine dependent and interested in quitting.