The purpose of this study is to learn more about the nicotine and non-nicotine chemicals that are part of e-cigarettes and their effects on cigarette smokers by assessing smokers' experiences with different e-cigarettes using a battery of self-report, biochemical, and behavioral indices. This is not a smoking cessation study; smokers will not be asked to quit smoking, and e-cigarettes will not be used as a medical device or therapy.