The proposed research will provide in-depth, longitudinal data, based on real-time reports, which will address key priorities for the FDA including, increased understanding of the relations between electronic cigarette (e-cig) use and 1) nicotine dependence, 2) reductions in combustible cigarette (CC) use, 3) attempts to quit CC use and the success of those attempts, and 4) health-related outcomes such as biomarkers of exposure and carcinogenicity.

Primary Aim: Characterize e-cig use patterns both acutely and over 2 years and relate them to patterns of CC use (including reduced CC use), nicotine dependence and related variables (e.g., withdrawal suppression), and attempts and success in quitting CC use. Investigators will use ecological momentary assessment (EMA) to obtain fine grained, real-time data on e-cig and CC use. These data will be used to test the hypotheses that increasing and higher levels of e-cig use, measured in real-time, will be negatively related to CC use, nicotine dependence, and CC withdrawal severity and positively related to CC quit attempts and CC cessation success.

Secondary Aim 1: Determine how the use of e-cigs is related to biomarkers of tobacco exposure and cancer risk, and to acute and chronic pulmonary health outcomes. Investigators will examine the relation between e-cig use and cancer biomarkers, exposure biomarkers, and pulmonary function.

Secondary Aim 2: Identify person factors, contextual variables, and patterns of behaviors and symp-toms that predict e-cig and CC use patterns and key outcomes (e.g., CC cessation, health-related outcomes), and identify variables that moderate relations between e-cig use and such outcomes. Investigators will attempt to identify contextual variables and person factors that predict increased e-cig use, decreased CC use (including cessation), reduced nicotine dependence, and significant changes in biomarkers and health outcomes. Further, investigators will identify variables that moderate such relations, revealing factors and events that make changes in e-cig and CC use, and associated outcomes, especially likely.

Inclusion Criteria:

• Specific eligibility requirements are:

  1. ≥ 18 years old
  2. able to read and write English
  3. no plans to quit smoking and/or e-cig use in the next 30 days
  4. not currently taking smoking cessation medication
  5. not currently in treatment for psychosis or bipolar disorder
  6. participants must report either that they have:

• smoked at least 5 cigarettes per day for the past 6 months and not used e-cigs within the last 3 months ("exclusive smokers")

• used nicotine-containing e-cigs at least once a week for the past month and have smoked at least 5 CCs/day for the last 3 months ("dual users").

Exclusion Criteria:

• Individuals not meeting any one of the inclusion criteria. Those not meeting any one (or more) of criteria 1-5 and either criterion 6a or 6b will be excluded.

2 groups: regular users of electronic cigarettes and commercial cigarettes and regular exclusive users of commercial cigarettes