Market Definition?

The 2010 horizontal merger guidelines issued by the antitrust agencies de-emphasize market definition, which has been a foundation of merger law for decades and was required by previous guidelines. The justification for this change is that unilateral adverse price effects caused by mergers of firms that produce differentiated products are best assessed using analyses that do not depend on market definition. Though the guidelines unquestionably serve a value in illuminating actual agency practice, any marginal benefit in dropping the exercise of market determination from the merger review process is likely to be small, and the marginal cost may be substantial.