This dissertation examined cognitive, emotional, and behavioral responses to different channels of political campaign advertisements in the social media context. Different channels such as social media platform (Facebook vs. Twitter), level of interactivity (high vs. low) and modality (visual vs. audiovisual advertisements) were manipulated as predictors of campaign learning, candidate evaluation, and political behavior. Several theories and concepts regarding interactivity (i.e., the theory of user control, the theory of structural isomorphism, the media richness theory, the social presence theory, cognitive load, and disorientation) and modality (i.e., the dual coding theory, the cue summation theory, the limited-capacity information processing theory, and multiple resource theory) were employed to investigate what conditions of modality and interactivity embedded within social media have the strongest effects on users’ cognitive, emotional, and behavioral responses in political campaign advertisements. Data were collected from 317 participants who completed the online experiment via Amazon Mechanical Turk. Findings demonstrated that interactivity, modality, and social media platform differently influenced campaign learning, candidate evaluation, and political behavior. Facebook generated greater campaign learning than Twitter without consideration of other factors such as interactivity and modality, and audiovisual advertisements generated greater campaign learning than visual counterparts. However, no significant effects of interactivity on political outcomes were found. Interestingly, however, under combined conditions of social media platform and modality, a significant interaction was found in campaign learning and candidate evaluation. Further, there were significant effects of social media when political, cognitive, and emotional involvement with social media were added as covariates, showing that Twitter generated more political behaviors than Facebook. Conceptually, the present study provides a better understanding of the validity of traditional theories about medium and communication channel, especially in the social media context, by reexamining different conceptualizations of medium, channel, mode of presentation, and media platform and by reviewing unique characteristics of social media. This study provides theoretical contributions to the understanding of cognitive, emotional, and behavioral reactions to different channels in the political campaign context by adding an explanation of the effects of interactivity and modality in relation to social media. Practically, the findings of this study may help candidates and political campaign practitioners build appropriate strategies for political campaigns through social media platforms to encourage their target publics to engage in political activities including political learning, candidate evaluation, and political behaviors.