This paper examines the strategies modern civic associations use to engage people in activism around health politics and develop civic leaders. Membership-based civic associations—such as the American Medical Association and Health Care for All—are pervasive in American politics. How do civic associations cultivate the broad and deep activism necessary for political power? The way people become mobilized for political activity affects who gets involved, what policy options are available for them to pursue, what policy coalitions can emerge, and, ultimately, the power different groups have in the policymaking process. Understanding how civic associations mobilize people, then, provides key insights into strategies these associations can use to affect policy.   I argue that strategic choices civic associations make about whether to pursue insider or outsider strategies in policymaking, and whether to centralize or distribute responsibility for engaging others affects how successful they are at engaging activists and developing leaders. Civic associations with the most active and engaged members are able to simultaneously go broad and deep in their development of new activists and leaders by investing in a core group of activists, developing their capacity to engage others, and drawing power from these people to mobilize others for activism. They do the hard work of investing deeply in activists and leaders only when they have to--in other words, when the strategic choices they made about how to build power to achieve their advocacy goals forces them to reach out to broad numbers of people.   This paper examines the way civic associations engage people through a study of two national, federated civic associations that mobilize citizens and doctors to get involved in health politics. The two-year study compared pairs of high- and low-engagement local organizations to identify the organizational characteristics and practices that distinguished high-engagement organizations. The study uniquely combines observational and experimental data to identify strategies that are most effective for engaging activism. This paper bucks conventional wisdom by arguing that organizations do not inspire activism only by charisma, message, or location. Instead, high-engagement organizations differentiate themselves through a set of organizational practices designed not only to reach the broadest possible pool of potential activists, but also to invest deeply in a subset of those activists and transform them into civic leaders.