This paper focuses on understanding the role of interest groups and markets in influencing regulatory change. To that end, it first identifies the interest groups surrounding the creation of legislation that separated commercial and investment banking in the 1930s and then identifies the interest groups involved in the more recent attempts to repeal the separation. Careful attention is also given to developments in the private market that affect the legislative process. This then becomes the case study for understanding how interest groups and market developments are able to influence regulatory policy. This particular case study finds that existing orthodox economic and political science literature gives too much credit to interest groups and not enough credit to private market developments when analyzing policy development and reform. Copyright 2001 The American Journal of Economics and Sociology.