Cigarette smoking is a leading cause of mortality in the United States and the foremost cause of cancer deaths. There are concerns that the decrease in cigarette smoking attained over the last several decades is now challenged by the increasing popularity of non-traditional tobacco products such as Electronic Nicotine Delivery Systems (ENDS), commonly referred to as e-cigarettes. The effects of ENDS use on public health are not well understood, including its plausible effects on cigarette use initiation, re-uptake, and maintenance. Currently, ENDS face limited regulations in the U.S. ENDS marketing in particular is not regulated. However, the prevalence of ENDS use is rapidly increasing, especially among young adults (18-25 year olds) who appear to be the main target of ENDS marketing. Current studies on ENDS marketing have been mostly qualitative, focused on characterizing the contents of advertising or retail marketing. These studies suggest that ENDS are being promoted to attract youth/young adults and as safer alternatives to cigarettes. But there is little evidence available on the effects of ENDS marketing on young adults' beliefs and attitudes and how those beliefs and attitudes promote ENDS use, and by extension, cigarette use. Elucidating the mechanisms of how ENDS marketing operates to impact young adults' ENDS use and smoking behavior could provide specific directions to the development of regulations on ENDS marketing as well as ENDS/tobacco control media interventions. For example, policies and media interventions could be informed as to which aspects of ENDS marketing need to be controlled and countered. This research will employ longitudinal design and the dual- process theoretical framework to determine the roles of outcome expectancies and implicit attitudes in explaining the effects of ENDS marketing on ENDS and cigarette use progression among college students, including cigarette use initiation and re-uptake. Guided by our preliminary research, we specifically focus on 4 positive outcome expectancies: social enhancement (e.g., use to gain popularity), affect regulation (e.g., use to regulate feelings), positive sensory experience (e.g., use to enjoy flavors), and positive health consequences. Consistent with the dual-process framework, which posits that spontaneous or automatic processes act parallel in decision-making to more conscious, reflective processes, we hypothesize that the effects of marketing on ENDS and cigarette use are mediated or explained by the 4 types of expectancies, jointly representing the reflective system, and by implicit attitudes, representing the spontaneous system. Spontaneous processes have never been assessed as mediators of the effects of tobacco product marketing on behavior in general and of ENDS marketing in particular. The multi-wave longitudinal design will facilitate rigorous causal inferences regarding the mechanisms of how ENDS marketing operates as well as help investigate marketing's role in young adults' changes in beliefs, attitudes and behavior over time. Thus, this research will employ powerful theoretical and methodological approaches and measures newly applied to ENDS research [e.g., Implicit Association Test (IAT)] to generate high quality information that currently does not exist.