Ever-increasing health spending, which, according to future projections, continues to outpace economic growth, will further endanger the financial sustainability of health systems. In a quest to improve the efficacy and efficiency of the health system and thus strengthen its financial sustainability, member states are employing market-based mechanisms to finance, manage, and provide health care. However, the introduction of elements of competition is constrained by the application of EU competition law, which raises significant concerns regarding the applicability of competition law and its limits in the field of health care. Due to the lack of a clear definition in EU legislation, the applicability and scope of competition law are determined on a case-by-case basis, which reveals an inconsistent approach by the European Commission and the CJEU regarding the application of competition law to health care providers and has created legal uncertainty. The aim of this article is to analyze relevant decisions by the commission and the CJEU case law in the pursuit of "boundaries" that may trigger the applicability of competition law with regard to health care providers. Based on the findings of the analysis, the article proposes a set of principles or guidelines for determining whether a health care provider should be considered as an undertaking and, as such, subject to EU competition law. Copyright © 2021 by Duke University Press.