This paper explores a new phenomenon at the intersection of digital networks and organizations—the Internet-based volunteer work force—people who use Internet applications to pursue a personal interest through volunteering contributions of time and talent that may create value for organizations and their customers or members. This work force is not centrally organized, managed, or measured. It is an emergent phenomenon resulting from discretionary small actions taken by large numbers of people, enabled by technology and human initiative. This paper proposes a general framework for understanding the phenomenon and offers an empirical investigation of one component of it—the role of feedback in producing and sustaining high-quality contributions from this work force. In a comparative study of Internet-based voluntary technical support groups for software problems, we found that in groups who implement systematic quality feedback systems (compared to those that do not), question askers return over a longer duration, answer providers contribute more often, and technical problem resolution is more effective. We also found that with systematic feedback, volunteers who produce higher quality contributions have longer participation duration, and participation duration is positively associated with community maintenance contributions.