Professionalization has become a given in the worlds of work and education. For a wide variety of professions, public and private organizations and training and further education courses, professionalization is an inescapable reality. However, it takes on diverse, even contradictory meanings, according to what it represents: a managerial imperative imposed by public or managerial policies, or a set of goals defined by an ideal of service or quality of work. The purpose of Encyclopedia of Professionalization is to discuss the current challenges facing professionalization and, by exploring major research traditions, to clarify the meanings associated with this concept and the various phenomena it encompasses. Three major notions of professionalization are examined: the manufacturing of professions in pursuit of autonomy, the rise of professionalisms embodying notions of a job well done, and the construction of renewed professionalities at the very heart of work situations and training systems.