This chapter examines how the changing roles and relationships between Professional Service Firms, clients and state actors in the context of broader social and economic transformations have challenged previously institutionalized forms of professional regulation. Although global Professional Service Firms have become both actors and arenas of regulation, the authors suggest that an exclusive focus on their self-regulation fails to do justice to the complex regulatory dynamics emerging at and across (sub-)national, regional, and global levels. Reviewing the literature on regulation in the accounting and legal professions the chapter shows that while competition, free trade, and quasi-market governance have expanded into a number of previously protected realms of professional organization and work, various state actors are reasserting their regulatory capacity in new multi-scalar actor constellations. These two closely interwoven trends develop against historically diverse legacies in different fields and countries.