Much of the literature on boards of directors of nonprofit organizations is prescriptive; that is, it describes what board members are "supposed" to do. The research described here looks at how members of thirteen human service boards actually play their roles. The findings indicate that some but not all board members play the role of trustee as it is described in the literature, that some board members combine the role of trustee with other roles (such as worker, expert, or representative), and that some play other roles to the exclusion of the role of trustee. The implications of the findings for organizational functioning, board performance, and accountability are explored.