My sense is that there is no need to revise the DOJ/FTC Horizontal Merger Guidelines, with one exception. As Greg Werden points out, “a thorough revision would take up to three years and occupy some of the agencies’ best people for a total of more than two thousand hours.” The current guidelines lay out the general framework quite well and any change in language relative to that framework are likely to create more confusion rather than less. Based on my own experience, the business community has had a good sense of how the agencies conduct merger analysis. The only exception is the Guideline’s concentration thresholds, which have been obsolete in practice since at least the mid 1990s. Those thresholds should probably be changed to reflect actual practice. If, however, the current administration intends to materially change the way merger analysis is conducted at the agencies, then perhaps greater revision makes more sense. But even then, perhaps the best approach is to try out some of the contemplated changes (i.e. in actual investigations) and publicize them in speeches and the like before memorializing them in a document that is likely to have some substantial permanence to it.