Although increasingly complex, modern innovation is still largely viewed through the lenses of sectors and distinct venues—e.g. large corporate R&D and new product development, entrepreneurial small or new ventures, or public programs or projects. However, Cleantech innovation is different—more blended, networked and boundary spanning. Social entrepreneurship and grassroots activism are also important. To understand such innovation emerging Cleantech activity in New York City—triggered by growing environmental concerns and opportunities due to rising energy costs—is studied. At a general level, Cleantech innovation decision making is viewed as a collaborative, complex set of activities involving diverse social entrepreneurs, grassroots movements, firms, public policy actions and hubs of innovation—all encompassing varied sectors and institutions and as a whole representing diverse individual backgrounds and motivations. Three grassroots NYC-based Cleantech endeavors are contrasted: vision42—a well-defined citizen-centric effort; Green Drinks NYC—a networking endeavor with no identifiable center (resembling a “meet-up”); and GREEEN.US—a fluid movement emanating from a university-based incubator and comprising diverse entrepreneurs, community activists, faculty, corporate executives and public officials. The lessons learned for Cleantech innovation and for modern innovation generally are then developed, focusing especially on the roles of social entrepreneurship and grassroots activism.