In June 2020, the Department of Justice and Federal Trade Commission released updated Vertical Merger Guidelines. Consistent with recent public debates on vertical merger policy, the new guidelines have been controversial, garnering both praise and criticism. Yet the development and longevity of past enforcement guidelines suggest that initial controversy itself is not a sign that the new Guidelines will be doomed to irrelevance or disuse. Guidelines that courted controversy when released, such as the 1982 Merger Guidelines, came to be recognized as an important evolutionary step in merger enforcement. Neither is unanimity a guarantee of longevity. A better predictor of the durability of prior agency guidelines has been the extent to which they reflect then-current FTC and DOJ enforcement practices. In this respect, the new Vertical Merger Guidelines appear well-positioned to serve as an enduring statement of enforcement policy.