This monograph addresses two problems surrounding the interpretation and application of Article 81 of the EC Treaty - what is competition and how does Article 81 ensure that competition is protected. After over 40 years of application and a period of modernisation, decentralisation, and reflection, it is possible to understand Article 81 and what it seeks to achieve. The monograph's aim is to reveal the intellectual order and rational structure underlying the law so as to enable the reader tounderstand Article 81 in a clear and rigorous manner. This is done by breaking Article 81 down into its constituent elements and examining the function that each element serves. Arguing that jurisdiction rests on a public/private distinction, both the substantive and the justificatory rules are cast to generate obligations appropriate for privateactors to perform. Actors and activities falling within the scope of Article 81 are subject to the substantive element prohibiting contrived reductions in output. Since output reduction can co-exist with cost reduction/innovation, and that these latter features are desirable, cost reduction andinnovation operate to justify infringement of the substantive obligation. Thus this monograph argues that output, cost and innovation are the only legitimate issues in an Article 81 analysis. It is in this sense that the monograph is concerned with the boundaries of Article 81 EC.