Who wins and loses in politics often depends on the relative strengths of competing groups. To increase their strengths and prevalence, groups often engage in mobilization efforts. How and when these attempts work is the topic of my dissertation. I take a micro approach by exploring the specific ways that varying rhetorical strategies enhance the likelihood of successful mobilization. Specifically, I combine rational choice and psychological theories to generate hypotheses concerning the role of thresholds (rules that determine how far the group is from its goal), the stakes involved in the decision, and source credibility in moderating the success of frames in increasing group participation. I then test these predictions in a series of three experiments---a voting game laboratory experiment, a mobilization survey-experiment, and a public goods laboratory experiment. I find evidence that group-based mobilization is most successful when moderators reinforce the mobilization messages, suggesting that identity-based politics have a greater underlying rational (i.e., instrumental) component than previously thought. The findings of this project have significant implications for the role of mobilization and identity in politics.