In this paper we consider more than three decades of research on teachers' unions in the United States. Focusing on unions' role in shaping education policy, we argue that collective bargaining and political organizing comprise the two central but distinct forms of influence at the district, state and national levels of decision-making. We note recent changes in state policy directly and indirectly affecting unions and union priorities. We argue that these changes may result in a variety of different conditions under which unions operate, and suggest that this variation represents fertile ground for new empirical analyses of union influence. Such work may in turn require a reconsideration of the extent of, and limitations to union power in altered educational landscapes.