Despite the impact that Internet-mediated advocacy organizations have had on American politics over the last decade, we are still learning about how they work. This is even truer for Internet-mediated issue specialists that focus on a single issue, such as climate change. Based on interviews with key staff members of two climate change advocacy campaigns, this article examines how these organizations communicate and mobilize citizens around their issue and the underlying assumptions behind their strategies. Interviews revealed a focus on like-minded issue public mobilization and online-to-offline social movement building strategies. The paper also examines how these organizations can influence policy debates by mobilizing issue publics, shifting debates to more favorable public arenas, and reframing them in ways more favorable to their causes. Implications for the future of climate policy and Internet-mediated advocacy research are discussed.