Jacques-Henri Jacot Changes in Work as Seen by an Economist : Regulations, Contracts or Institutions ? Defined as the interrelation between, on the one hand, work, its content, organization and conditions and, on the other, the labor force, its qualifications, training and management, the «system of work» has undergone a crisis over the last two decades. To what extent can theories of regulation and contractualization account for the changes that have occurred ? The concepts developed by these theories restrict them to, respectively, macro-and microeconomics. Combining these two approaches also raises problems. The suggestion is made to heed, instead, American institutionalist economists. In their program of research, informal and formal ...