This dissertation seeks to understand how issue publics contribute to citizen competence and the functioning of democracy. In the first part of the dissertation, a new measurement was constructed by theoretically and empirically analyzing the attributes of issue public members. Through the hypotheses testing, the new measure was more reliable in identifying issue public members compared to previous measurement strategies. Employing the new measure, results show that issue public members with concern about a specific issue, exercised their issue-specificity in seeking information (i.e., issue-based selectivity) with exposure to both attitude-consistent and counter-attitudinal perspectives. Issue public membership also had significant effects on issue-specific knowledge, and generating rationales for their own and other's oppositional viewpoints. These direct effects were mediated by issue-based selectivity. The relationships highlight the importance of issue publics in contributing to the deliberative democracy. In addition, issue publics play a significant role in contributing to the participatory democracy in that issue public members have greater intentions to participate in issue-related activities than nonmembers. However, while issue publics come close to solve the deliberative-participatory paradox, it was found that their information selectivity and argument generation were unbalanced in a way of favoring pro-attitudinal perspectives over counter-attitudinal perspectives. The second part of the dissertation examined conditional factors--accuracy and directional goals in affecting information selectivity and processing. The findings show that directional goals influenced participants to apply either the strategies of selective approach or selective avoidance to seek information depending on the issue. Accuracy goals exerted a main effect on the issue that is relatively less controversial and less obtrusive. They also interacted with issue public membership in influencing the less controversial and less obtrusive issue. Argument generation was not affected by accuracy or directional goals. Overall, through conceptualizing citizens as members of different issue publics, individuals are more competent then we thought. Their intrinsic interest in an issue serves as a strong factor affecting their information selectivity, information processing, and political actions. Despite finding an optimistic role for issue publics in the democratic process, their limitations also should be recognized. The implications for the deliberative and participatory democracy are discussed.