Volunteer activity is work performed without monetary recompense. This article shows that volunteering is a sizeable economic activity in the United States, that volunteers have high skills and opportunity costs of time, that standard labor supply explanations of volunteering account for only a minor part of volunteer behavior, and that many volunteer only when requested to do so. This suggests that volunteering is a "conscience good or activity"-something that people feel morally obligated to do when asked, but which they would just as soon let someone else do.