Governance has long been a central theme in the literature on professional service firms (PSFs). Previous studies have presented dichotomized models of organisational archetypes and legal form: professional partnership versus managed professional business, adhocracy versus professional bureaucracy, partnership versus corporation, private versus public corporation. The current working paper argues that these dichotomised models ignore the variety of forms of governance prevalent within the professional service firm sector- in reality a professional service firm will adopt multiple forms of governance over time in response to its increasing scale and complexity. The study asks: how does governance change over time as a professional service firm increases in size and complexity? Adapting Greiner's classic model of the stages of organisational growth (1972, 1998) this chapter presents a multi-stage model of governance in professional service firms, highlighting the crises and reversals that may occur as firms pass through these stages. The study goes further to illustrate the complex and messy reality of the process of evolution in the governance of a professional service firm by presenting two cases: a small, young corporation and a long-established, large global partnership. These cases emphasise the crises and reversals that can occur during aborted attempts at governance change. The chapter concludes by analysing the key conceptual differences between Greiner's generic model and the PSF-specific model presented here and argues that these differences are associated with the distinctive nature of power dependencies within a professional service firm.