Groups are often mobilized to take action in politics. For example, the civil rights movement of the 1960s and other social movements illustrate the large role that group mobilization plays in politics. Further, in election contests and policy debates, political elites and campaigns often target the group identities of voters to mobilize group support. However, while group-based mobilization is clearly widespread in politics, social science theories have little to say about which group-based mobilization strategies are likely to work and in what circumstances. This gap in our understanding of group-based mobilization stems from a divide in the field between explanations of decision-making that emphasize individual costs/benefits analysis (rational models) and those that emphasize attachment to group (group models). This project seeks to fill this gap by merging group-based models with the rational choice model to provide an empirically testable theory of when and how group-based mobilization efforts increase participation. Since individuals who strongly identify with their group are likely to participate in group efforts regardless of mobilization efforts, the key question is: what factors make individuals who moderately identify with their group susceptible to group-based mobilization attempts? Frames in political communication (i.e. persuasive messages containing interpretations of events) have been shown to change individuals? opinions or behavior and can be used to mobilize groups if the frame targets group identity. However, an underlying rationality determines whether individuals with moderate predispositions (such as group identity) will accept or reject frames. This rationality is captured by factors, or moderators that limit framing effects, that help us predict whether individuals will accept or reject frames (Druckman, 2001a; 2001b). As such, a study of group frames and potential moderators can help generate testable predictions and merge rational and group-based models of behavior. This project seeks to demonstrate that successful group-based mobilization efforts consist of frames that target group identity and that are reinforced by moderators, such as thresholds (rules that determine how far the group is from their goal), credible sources of mobilization messages, the stakes involved in the decision, and the interactions among these factors. The results from an initial voting game laboratory experiment for the first part of the dissertation provide support for the hypothesis concerning the interaction between group-targeted frames and the moderator of thresholds. This research is supplemented with a public goods laboratory experiment that tests the effects of group-targeted frames, stakes, and credible sources. In addition, a survey-experiment has been developed that tests group-targeted frames and support for a school bond proposal. This project helps us understand the role of group identity in politics, and this is important to understand for three key reasons. First, this project helps us understand which types of mobilization strategies increase participation of underrepresented groups, such as minorities and females. Secondly, the findings of this project suggest that mobilization strategies do not have to include content that increases intergroup tensions. In other words, this project highlights that group strategies can increase participation of group members without also increasing intergroup tensions. Finally, this project opens the door for future explorations of strategies for diffusing intergroup tensions, particularly in situations where these tensions are high and could involve violence or conflict.