Interpersonal communication has been shown to directly and indirectly influence various health behaviors, including smoking-related outcomes. However, the literature in this domain has mostly measured interpersonal communication as face-to-face conversations, and has treated such instances of communication as distinct from online forms of person-to-person communication. This dissertation is aimed at exploring sharing – an all-encompassing concept of person-to-person communication that covers both offline and online forms of communication – in the context of tobacco and e-cigarette communication, through three separate studies. Study 1 was a validation study that assessed the reliability and validity of a newly proposed sharing measure, providing a valid measure that could not only be used in the subsequent studies of this dissertation but also in future studies examining sharing in the tobacco and e-cigarette domain. In an effort to explore the nature of sharing, Study 2 examined the determinants of overall tobacco and e-cigarette sharing as well as sharing positive vs. negative tobacco and e-cigarette content. Findings showed that personal relevance and exposure to relevant information predicted sharing, and that personal relevance and normative perceptions interacted in their effects on the valence in which people shared. Study 3 was aimed at examining the consequences of sharing about tobacco and e-cigarettes. Specifically, it examined the direct effects of sharing on future intentions and behavior, as well as the contingent effects of sharing and pre-existing intentions on future behavior. Findings showed that sharing positive content predicted increased likelihood of intending to use and actually using tobacco and e-cigarettes. Furthermore, sharing consistently with intentions amplified the effect of those intentions on future behavior, while sharing inconsistently with intentions predicted reduced effects. Possible explanations for findings and potential areas for future research are discussed.