Progressive religious leaders are playing an increasingly important role in the effort to combat climate change. Through a combination of unstructured in-depth interviews and primary source analysis, this thesis highlights nine U.S. religious leaders from various denominations of Christianity, Judaism and Islam who are actively involved in working on climate issues. Drawing on literature in social movement theory, I explore how clergy are uniquely influential in climate issues because of the organizational advantage and moral authority they hold through their positions as religious leaders, granting them the ability to highlight social justice implications of climate change with distinctive legitimacy. Clergy engage in climate issues through a number of tactics and myriad activities spanning three domains: their congregations, the climate movement, and policy circles. While religious leaders are imbued with moral authority that allows them to speak powerfully on the social justice implications of climate change, they are also limited in a number of ways precisely because they are working within a religious context.