Basic as it has become to studies of the Japanese economy, the concept of the "Keiretsu" is sheer fiction -- a creature of the academic imagination with no basis in real economic behavior. Almost all scholars writing on the subject use the categorization found in the annual Keiretsu no kenkyu [Research on the Keiretsu]. Published by an otherwise unknown Marxist "research institute" since 1960, the volume purports to sort firms by functional groupings. In fact, it simply sorts them by their principal loan source. If that loan source proxied for some unobserved variable, this sorting might be helpful. In fact, it does not. For example, among keiretsu firms, there is little cross-shareholding. Indeed, the non-financial firms in a given keiretsu hold stock in few other keiretsu firms at all. Although financial firms do buy stock in their debtors, they seem as likely to buy the stock of their non-keiretsu debtors as of keiretsu debtors. The lending patterns of financial firms in a keiretsu are usually uncorrelated, and much the same is true of their shareholding patterns.