["Journal for the Scientific Study of Religion, EarlyView. ", "\nABSTRACT\nMuch of the activism on environmental issues within the US Catholic Church is not coming from those with institutional power (like bishops and diocesan priests), but rather from sisters, who have no formal power. What factors facilitate sisters’ environmental activism? Drawing on qualitative interviews with US Catholic sisters who are leaders in environmental activism, we find that characteristics of avowed religious life, particularly sisters’ social networks, communal life, and biographical availability, facilitate their mobilization. Findings also suggest a relationship between institutional power and activism, with sisters’ relative lack of power giving them freedom in the margins to engage in activism. In contrast, environmental activism among bishops and priests may be constrained by their greater isolation from community and greater institutional power, which they seek to protect. This research contributes to literature on religion and social movements, as well as highlighting gendered power dynamics and environmental politics in the Catholic Church.\n"]