What professionalisation means has to be clarified in relation to the terms profession, professionality and professionalism. Is it about an occupation becoming a profession or about the individual development of professionality or about the formation of a professional identity? These questions are discussed systematically from the point of view of general educational science, complemented by a historical view of the development of teacher education and training in Germany. It is no surprise that the conceptualisation of professionalisation is contested. Against this background the importance of a clear conceptual basis is emphasised both for national and especially for international-comparative research.