This paper seeks to explore and explain the dramatic organizational changes that took place over a relatively short time period in the five largest global professional networks (GPNs) - a group of organizations that were originally global accounting firms and traditionally accustomed to relatively gradual change. Data were collected from the firms' Web sites, interviews with GPN managers, e-mail requests for information via Big Five Web sites, and from reports in the newspapers and business press over the two-year period to June 2001. The paper uses neo-institutional theory to study the context, precipitating dynamics, and enabling dynamics of large-scale organizational change, including the part played by government and regulatory forces. The study explains the extent to which changes have occurred in a sample of countries in which these organizations operate, noting that the firm effects seem to be stronger than the country effects in the consulting area, while country effects are more pronounced in the law area.