This article contends that teacher unions' participation in policy making during South Africa's political transition was characterised by assertion of ideological identity (unionism and professionalism) and the cultivation of policy networks and alliances. It is argued that, historically, while teacher unions were divided along political and ideological lines, they have demonstrated flexibility in contesting for influence in the policy arena. In this regard, teacher unions' agency plays an important part and is reflected in changes in organisational strategies to ensure their independence or prevent marginalisation. The article highlights the threat of state co-optation for teacher unions and suggests that a framework for managing teacher union--state relations based on 'professional unionism' could potentially contribute to more effective education service provision. Comparisons with teacher unions' experiences elsewhere in the world are also made, while recognising the specificity of the South African situation.