The United States Department of Justice, Antitrust Division, and the Federal Trade Commission have released new merger guidelines explaining how the enforcement agencies review horizontal mergers. The merger guidelines have existed in various forms since 1968. The last major revision was in the mid-1990s. The agencies announced last fall that they were planning to revise the guidelines. A series of workshops followed at which input was sought from the bar and the public. Draft guidelines were released for comment last spring. These guidelines constitute a substantial departure from previous guidelines, particularly with respect to the reduced role of market definition. The guidelines can be accessed on the Antitrust Division’s website and by clicking here.