AbstractThis article proposes two broad ways to conceptualise EU competition law. EU competition law could be viewed as ‘autonomous law’ (‘AL’), namely as a closed normative system a technocratic tool consisting in a set of rules that prohibit undue restraints of trade. Or, EU competition law could be viewed as ‘responsive law’ (‘RL’), namely as a relatively open normative system and an interpretive practice that oscillates between openness and integrity. The responsiveness approach offers a compelling conceptualisation as it explains certain endogenous features of EU competition law: its fuzzy mandate, conceptually elastic vocabulary, and use of rules and standards. In addition, the responsiveness approach can clarify the role economics plays in EU competition law. It views economics as an ‘ideological science’, which, even though it cannot insulate this legal field from value disagreements and make it ‘autonomous’, it can provide a source for positive and normative interpretive statements. On this basis the responsiveness approach maintains that EU competition law is by design open—ie conceptually elastic and factually sensitive—and that its openness can enhance, but also undermine its integrity—ie its capacity to realise its objective in a rule of law compatible manner. These conflicts between openness and integrity are the cause of EU competition law's relative indeterminacy. To deal with the problem of indeterminacy, the RL approach proposes a tripartite legal-institutional modus operandi consisting in constructive interpretation, responsive enforcement, and catalytic adjudication. Hence, considering EU competition law as a form of responsive law has three major implications: first, it offers a new way for understanding how this legal field works and changes; second, it suggests a strategy for dealing with EU competition law's indeterminacy, and third it proposes a new framing for the discursive practices of EU competition law's epistemic community.