This paper describes an emerging aspect of Japanese industrial organization and inquires into the nature of the entrepreneurship operating therein. Posing the problem in this way immediately raises one fundamental question. That is, are there any temporal or national variations in the pattern of entrepreneurial behavior in modern firms? My own answer to this question, as presented here, is simply in the affirmative. I will submit that, from the beginning of the 1970s onward, the most important function of the entrepreneur has become that of adapting the internal structure and external behavior of firms quickly, flexibly, and innovatively to increasing environmental uncertainties caused by such factors as supply shocks, the new opportunities that have opened up for technological innovation, the absolute as well as relative variability of prices, interest rates, and exchange rates, etc. I will further argue that Japanese firms have responded to this task by developing a rather new form of industrial organization, which I will term the "quasi-tree structure."