Taking the latest reform of Swedish teacher education as a point of departure, the aim of this article is to analyse the way Swedish teacher unions construct a knowledge base for teaching as a strategy of professionalisation. The analysis shows that the unions construct such a knowledge base from opposing points of departure. Their professional ambitions are, thus, challenged by processes of intraprofessional boundary work complicating the construction of a unanimous "voice" of teachers in Swedish education policy debates. This intraprofessional struggle over the meaning of teacher professionalism underlines the political nature of the use of professionalism in the transformed welfare sectors of today. In this respect, the article also underlines the importance of tradition in discussions of what is to be considered a professional teacher. Despite decades of political ambitions to unite Swedish teachers into one single profession, the historical differences between two separate teacher identities continue to fundamentally affect the policy positions of the teacher unions--a development that the recent reorientation of Swedish education policy seems to reinforce. As a result, the usefulness of talking about Swedish teachers as a single profession in the future may be questioned.