This is a qualitative study of collective action at a large American university. The project explores the motivations for civic engagement of individuals. Eighteen respondents that had been involved with a Sustainability and Greening (SAG) council were interviewed with a biographical in-depth interview approach using an open-ended interview guide. Data was analyzed deductively using Diffusion of Innovations theory as a guide. Categorizing individuals according to Diffusion of Innovation adopter categories proved useful in understanding motivations to engage. Results show that individuals went through an innovation-decision process and were motivated by perceived compatibility of the SAG council collective action with their prior knowledge and current social context, relative advantages of the SAG as an innovation, and most notably by opinion leader endorsements. The study contributes to collective action research by showing how actors can be differentially motivated over time and how engagement can be nurtured to meet our looming social problems.