The notion of ‘distortion of competition’ is a central yet variably interpreted concept within EU competition policy. While the term generally implies a deviation from a fair competitive business environment, its legal and operational meaning diverges substantially across different branches of EU competition law. This chapter provides a systematic and comparative analysis of how distortion of competition is defined, interpreted, and applied in the three traditional domains and one more nascent domain, i.e. antitrust, merger control, State aid policy, and the more recent regulation of foreign subsidies. Starting from the respective legal bases, it examines how each area conceptualises competitive distortion, drawing also on decisional practice, milestone cases before the EU Courts, as well as academic literature. Through this cross-pillar examination, the chapter identifies both commonalities and divergences in how the concept is deployed and enforced in the traditional competition areas and reviews its meaning in the more recently introduced regulation on foreign subsidies. The analysis reveals that while all branches aim to ensure fair competition in the internal market, the notion of distortion is neither uniform nor interchangeable. This raises important questions about coherence and legal certainty, and suggests the potential benefits of a more integrated approach.