Introduction Is the concept of “companyism,” introduced by the régulationist approach to describe the mode of régulation in Japan from the 1950s to the 1980s, still accurate to understand the Japanese economy in 2010? In this chapter, our answer is negative because of the following stylized fact: the increasing heterogeneity of Japanese firms during the Lost Decade (1991-2002).The critical point of our argument does not concern the static heterogeneity of firms but its evolution. Moreover, we emphasize that this increasing heterogeneity concerns performance and organization of firms of similar size and they belong to the same narrow sectors. It does not mean that the former companyist compromise completely disappeared: it still exists for core workers in some large firms as explained by Yamada and Hirano in Chapter 1. However, it is no longer possible to find companyist regularities at the micro level in order to define the mode of régulation in Japan. It is true that even in the 1970s, this compromise did not concern all Japanese firms, not even all large firms; however, the main difference between that time and the current period is that it was the norm. More importantly, this predominance had significant macro effects (e.g., for productivity dynamics). In this paper, we argue that the Japanese economy has reached a threshold beyond which the companyist compromise no longer plays its role at the macro level. Consequently, it does not help to define the Japanese mode of régulation. Therefore, we propose to go one step beyond the analysis of Yamada and Hirano in Chapter 1: companyist compromise is not only dysfunctional but has also lost its previous role at the macro level, which used to define the mode of régulation in Japan.1