Specific historical events and conditions have alternately increased and decreased supply and demand relating to volunteers. Recent influences on volunteerism include recruitment from new segments of the population and the women's liberation movement. As a result, the roles and responsibilities of volunteers are being broadened and redefined. Recent data show that volunteers constitute approximately 20 percent of drug abuse program personnel and are most heavily involved in counseling functions. Surveys of volunteers' background characteristics reveal that there is no typical volunteer. Volunteers do share certain personality characteristics, however, including concern for the welfare of others, desire to help, empathy, enthusiasm, dedication, honesty, sincerity, tolerance, objectivity, and flexibility. Motives for volunteering include both altruism and self-interest. Both qualitative and quantitative evaluations give evidence that volunteers are successful, and volunteers as well as clients benefit from the volunteer experience. Although staff are initially skeptical, they usually have positive reactions after observing volunteers' interactions with clients. Administrative concerns in the implementation of successful volunteer programs include outreach to various population segments as sources of volunteers, and adaptation of training and deployment practices to meet program needs as well as the particular talents and inclinations of individual volunteers. Including community members in all phases of program planning and development is vital. The literature contributing insights and approaches to volunteer involvement stems from the fields of mental health, corrections, alcoholism treatment, health care, education, and social service. A bibliography listing 337 references and an appendix presenting bibliographic documentation of functions and activities performed by volunteers are included.