In December 2023, the Department of Justice and the Federal Trade Commission issued the eighth iteration of the Merger Guidelines—guidance documents that outline the antitrust agencies’ priorities when reviewing a merger or acquisition. These documents are not legally binding. And yet over the past fifty years, courts have heavily relied upon the Guidelines to decide antitrust cases, citing them in equal breath with statutes and case law. This is a deference that has unfolded quietly. Courts piling on citations to the Guidelines have not articulated exactly what kind of deference these guidance documents are receiving. Nor have they explained why this deference is happening at all.

This Note seeks to shine a light on how and why the Merger Guidelines climbed to such an incredibly prominent position in modern antitrust jurisprudence. First, it charts the history of the Guidelines’ birth and development from 1968 to 2023, highlighting how the Guidelines and the case law gradually came into conversation with one another. It then explores how the antitrust agencies came to voluntarily adopt notice-and-comment procedures that mimic the Administrative Procedure Act’s requirements, despite having no obligation to do so. This Note argues that the agencies have sought to cloak the Guidelines in greater procedure in order to bolster their popular legitimacy and temper judicial skepticism. After categorizing the specific language judges have used to refer to the Guidelines in merger decisions from December 2000 to February 2025, this Note concludes that courts have generally failed to label their deference. From this silence, the Note predicts courts will continue to rely on the Guidelines and argues they should apply Skidmore deference when doing so. This Note closes with an exploration of whether the Supreme Court’s doctrinal tidal waves in deference and finality might uproot the thus far nameless deference. The first year of cases issued under the 2023 Guidelines reveals that the Guidelines have largely remained persuasive to the courts. Antitrust’s north star continues to light the way.