The organizational field that constitutes English rugby union has undergone substantial change since 1995. This paper builds on earlier work by O'Brien and Slack (2003a) that established that a shift from an amateur to a professional dominant logic in English rugby union took place between 1995 and 2000. Utilizing ideas about institutional logics, isomorphism, and diffusion, the current paper explores how this shift in logics actually evolved. Data from 43 interviews with key individuals in English rugby union form the main data source for the study. The results show that isomorphic change in accord with a new professional logic diffused throughout the field by way of three distinct diffusion patterns: status driven, bandwagon, and eventually, the social learning of adaptive responses. An initial period of high uncertainty, intense competitive pressures, and sustained financial crises resulted in unrestrained mimesis in the first two seasons of the professional era. However, this gave way in the third season to increased interorganizational linkages, coalition building, and political activity that promoted normative and coercive pressures for a consolidation of the game's infrastructure and future development.