Various attempts to specify the nature of professions in general and of teaching in particular in relation to the knowledge that is needed for practice are considered. It is argued that there is no epistemic or moral criterion of professionalism that will sustain the claim of teaching to be a profession. The nature of teachers knowledge is examined and the relationship between theory and application is seen to be both crucial to and problematic in our understanding of the nature of teachers work. The implications of the discussion for teacher education are assessed.