Antitrust enforcement has a crucial role to play in consolidated health care markets as providers undertake mergers, acquisitions, and other types of collaborations to integrate care and achieve greater size and scale. But antitrust enforcers and policy makers need to refine their approach in two fundamental ways. First, in addition to focusing on whether particular transactions or conduct will increase prices above competitive levels, a more pressing concern should be on assuring that health care markets are conducive to fundamental changes in how care is reimbursed and delivered — that is, the impact on payment and health care delivery innovation. Second, it is important to recognize the practical limits that apply to antitrust enforcement, both in terms of existing law and precedent and the constrained resources available to government enforcers. Government resources can be leveraged substantially through greater collaboration among federal and state antitrust enforcers, government payers, health care regulators, and economists and other policy makers. This can result in not only better-targeted antitrust enforcement actions but also payment and regulatory initiatives that can produce better-functioning and more competitive health care markets.