In the first half of the twentieth century, the merger among American businesses was horizontal - the acquisition by one company of one or more of its direct competitors. More recently, however, non-horizontal acquisitions have tended to predominate. These transactions have taken the acquisition by a company of either its supplier or its customer, and of conglomerate mergers, i.e., the acquisition by a company neither in direct competition with, nor a supplier to or buyer from, the acquired company. The merger decisions in the courts most pre-1965 Clayton Act section cases involved horizontal acquisitions, in the late 1960's and early 1970's much merger jurisprudence was devoted to the analysis and treatment of non-horizontal mergers. The past two decades have also witnessed substantial scholarly interest in the development of various theories for testing the effect on competition, and hence the legality, of these non-horizontal acquisitions. Particular attention has been focused on conglomerate mergers. Furthermore, the Department of Justice and the Federal Trade Commission have increased the attention and enforcement efforts given to these kinds of transactions. The growing concern about conglomerate mergers was reflected in part in the Guidelines promulgated the by the Department of Justice in 1968, which detailed the kinds of acquisitions that might be the subject of governmental challenge. In the intervening fourteen years, however, challenges to most conglomerate mergers received relatively hostile treatment from the courts. Many scholars criticized the soundness of the theories used to challenge these transactions and suggested that most such acquisitions will not in fact adversely affect competition. In 1982, largely in reaction to these developments, the Department of Justice promulgated new Merger Guidelines, indicating that it will not challenge non-horizontal mergers, unless the transactions are likely to have an adverse impact on actual or potential competition. The practical result of this policy is that most such acquisitions will be allowed. This development was predictable, since the Assistant Attorney General heading the Antitrust Division, William Baxter, had on several occasions stated that most non-horizontal restraints have insufficient adverse effects on competition to merit Justice Department attention. Thus, it is hardly surprising that the new Guidelines focused principally on horizontal mergers, and disapprove non-horizontal mergers only to the extent that they may diminish horizontal competition. This Article argues that the Department of Justice's recently articulated enforcement intentions with respect to conglomerate mergers are inconsistent with the case law applying section 7 of the Clayton Act to these transactions and also represent unsound policy. Part I will review the conglomerate merger jurisprudence of the past two decades - looking at the theories that have been used to challenge them, at the important judicial decisions interpreting and applying those theories, and at the Guidelines adopted by the Department of Justice in 1968 to codify these developments. It will then briefly discuss certain developments regarding conglomerate mergers the past half-dozen years - the judicial rejection of most challenges to these transactions, scholarly attacks on the underlying theories, and the enormous expansion of the number and size of conglomerate mergers taking place. Part II will then examine the new Merger Guidelines. The way in which the new Guidelines treat conglomerate mergers will be compared with the case law standards and with the 1968 Guidelines. Based on a broad view of the goals of the antitrust laws, this Article will then assert that the Guidelines take far too narrow an approach to the scrutiny of conglomerate mergers. The Article will conclude with some recommendations for future conglomerate merger law enforcement.