Drawing on a study of members of the U.K. National Union of Teachers, this article considers the extent to which economic exchange, social exchange, and covenantal considerations underpin union members’ willingness to continue membership and to participate actively in their union through union citizenship behaviors (UCB). Findings suggest that the more activist forms of UCB were motivated primarily by a perceived covenantal relationship with the union. In contrast, exchange, particularly social exchange, motivations played more of a role in motivating less demanding “rank and file” UCB and intent to quit the union. Union instrumentality appeared to be a necessary but insufficient condition for union viability, having an indirect effect on UCB and intent to quit the union and also moderating the effects of pro-union attitudes. Implications for union strategy are considered.