Environmental issues are particularly salient for today's generation of young adults. Indeed, many have suggested that it will be this generation that will lead the environmental movement forward. Therefore, this study examines the motivations and mechanisms that influence proclivity and intensity of young adults' environmental volunteerism. Using a survey of environmental attitudes and behaviors of college students at a large urban Canadian university (n = 1 372), we assess why today's young adults volunteer for the environment and the factors that motivate their commitment. Our findings suggest that young adults who engage in pro-environmental behaviors in general, as well as those who volunteer for other types of nonprofit organizations, are more likely to volunteer for environmental nonprofit organizations. Moreover, we find that social aspects of volunteering are the strongest positive predictor of the intensity of volunteerism in environmental groups. Copyright © 2011 John Wiley & Sons, Ltd.