In 1958, the first Museum act for local and regional history museums was passed in Denmark establishing a subsidiary system and defining a set of criteria for what constituted professional museum work. Since then, Danish museums have developed from single-curator institutions to diverse professional workplaces with a number of cooperating specialists. Based on empirical studies, this project has tracked the changing definition of professionalism from 1958 until 2018 by examining the development of the Danish museum legislation, the description of professional museum work and the related skills as well as the training and education offered to museum professionals. Moreover, it explores museum mediation as a specialized field within museum work and the museum mediator as an emerging specialist throughout the period.Thus, the project offers an interpretation of the contemporary history of the Danish museum field and of professionalism in a significant part of the cultural sector in Denmark.