About million people, or 27.6 percent of the civilian noninstitutional population, volunteered through or for an organization at some point from September 2001 to September 2002. Volunteers are a major source of labor in the United States, performing a variety of important tasks and contributing considerable time and effort to meeting the needs of their communities. The data in this article come from a special supplement to the September 2002 Current Population Survey (CPS).(1) The supplement collected information on the incidence of volunteering, the number and type of organizations through or for which persons volunteered, total hours spent volunteering, how people became involved in volunteering, and the kinds of work they performed as volunteers.