Many scholars have documented the important role of national environmental groups in affecting environmental policies in the United States. The role of local environmental groups, however, has not been thoroughly documented. Using data from a complete census of all environmental groups in two Vermont counties, we :(1) offer a set of conceptual categories for local environmental groups; (2) analyze how civic engagement in these groups is creating different forms of social capital through stewardship activities, education and communication, partnerships with other organizations, and alliances with public agencies; and (3) explore how these groups are affecting the policy process, illustrated with two case studies. We argue that the prevalence and contribution of local environmental groups, particularly local autonomous groups, has been underappreciated. We conclude that the greeining of social capital is significantly affecting environmental outcomes in the United States.