Society in Northern Ireland can be characterised as being underpinned by an enduring cultural, religious and political divide between two dominant communities: Catholics and Protestants. The educational system largely reflects and contributes to the reproduction of this separation. Teachers are generally deployed in schools that are consistent with their community identity. Teaching is a very heavily unionised profession, but there has been very little research conducted into the manner in which the community divide has affected the character and composition of the unions that represent teachers in NI. This mixed method investigation addresses that gap in knowledge. It is revealed that although sectoral separation is a significant feature of the profile of union membership, there is considerable consensus with regard to the unions' stance on the policies that maintain the pattern of teacher deployment. The composition of two unions in particular is ideogrammatic of the community division in education. It is noted however that a combination of economic, political and social factors has contributed to a pragmatic re-configuration of old alliances and rivalries. This realignment has the potential to ensure that teacher unions remain relevant and serve the needs of their members in a post-conflict society.