Over the last fifty years, professions have been subject to a radical transformation triggered by large-scale processes of change such as the post-industrial transition, globalisation, and digitalisation. In this changing context, knowledge has become a strategic factor in production, and those who have control over it now play an increasingly important role. Accordingly, the number of people that define themselves as “professionals” has grown at a steady pace. However, they have undergone processes of differentiation that have led to increasing heterogeneity. This introductory chapter addresses the above issues by introducing an analytical framework that identifies three dimensions along which this differentiation may be developed—within, between, and beyond (WBB)—also referred to as the WBB model. Each dimension focuses on a specific set of phenomena either occurring inside a profession, across professional groups, or regarding professionals’ relationship with society at large. Combined, the three dimensions provide a detailed picture of the changes that are taking place worldwide in the field of professions. After defining the fundamental concepts used and highlighting the impact of the above processes of change on professionalism, the chapter gives operative definitions of the three dimensions and then provides an outline of the chapters collected in the book.