Mobile media offer new opportunities for fostering communications between individuals and companies. Corporate websites are being increasingly accessed via smart phones and companies are scrambling to offer a mobile-friendly user experience on their sites. However, very little is known about how interactivity in the mobile context affects user responses to media content. In order to fill this gap, this dissertation investigates the effects of two types of interactivity upon individuals' attitudes toward mobile websites as well as relational outcomes. An online 2 (modality interactivity: high vs. low) x 3 (message interactivity: control vs. low vs. high) between-participants factorial experiment was conducted. Modality interactivity was operationalized in terms of the number of interaction techniques employed in a mobile website, whereas message interactivity was operationalized as the degree to which the interface displayed message exchanges in a threaded manner. Findings from this study suggest that users psychologically discriminate between the different interaction techniques available on mobile websites. When individuals were given various ways of interacting with the website content (i.e., high modality interactivity), they were more likely to express enjoyment and be engaged in website interaction, which in turn yielded better website attitudes and behavioral intentions. Modality interactivity also significantly predicted relational outcomes, and this relationship was mediated by enjoyment and user engagement, with the former preceding the latter. In the case of message interactivity, the analysis revealed two psychological processes leading to positive website attitudes and website behavioral intentions: a cognitively effortful process via perceived contingency and dialogue and a heuristic process via perceived contingency and enjoyment. Furthermore, the level of power usage moderated the effects of the two types of interactivity on negative outcomes, including perceived bells and whistles and perceived distractions. Individuals scoring lower on power usage showed more negative outcomes when the mobile website offered higher level of interactivity, while the opposite was true for individuals scoring higher on power usage. In general, power users prefer interactivity features more than non-power users. Theoretical as well as practical implications of these findings for the study of mobile interactivity in a public relations context are discussed. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]