In the foreword, it is submitted an initial distinction on competition between companies and competition between jurisdictions. This is followed by an analysis of types and methods of competition between jurisdictions leading to the conclusion that tax competition (an ambiguous concept) represents a form of institutional competition. On the follow-up of the analysis of the methods, objectives and sources of tax competition, one considers the social, economic and political conditions which made possible the emergence and assertion of this topic in Europe. Finally, one presents the distinction between harmful and fair tax competition from an OECD and European Union point of view, questioning the real nature of such distinction. Title I ( Tax competition between economics, law and politics ) endeavours to provide an answer to the above question, by examining the topic of tax competition from three different perspectives: economic, legal and political. To this effect one presents the main economic theories on tax competition, in particular those of Tiebout, Oates, Zodrow and Mieszkowski and the school of public choice followed by their proposed evaluation of tax competition and its consequences. Even if it is possible to outline certain main trends on the role and effects of tax competition, the results of economic studies are not conclusive. Thus, it is difficult to set a clear border between harmful and fair tax competition and, consequently, to justify, exclusively from this point of view, the regulation of tax competition. The same can be argued from a strictly legal perspective. In spite of several attempts by certain authors and by the European Commission to present the fight against harmful tax competition as a consequence of the objectives of the Treaty, the truth is that, tax competition remains the standard and the Treaty does not lay down a clear distinction between its positive and negative dimensions . Even if one accepts, as a working hypothesis, the distinction established by the Commission on this issue, one has to conclude that the Community economic constitution does not contain adequate instruments to counter harmful tax competition. In fact, neither the Community legal principles, the Commission powers to control State aid, the Treaty articles on competition distortions (96 and 97) nor the rules on economic and monetary Union were drawn up for this purpose. The history of the Community tax policy reveals that the distinction between harmful and fair tax competition as well as the present pursuit of regulating this phenomenon rises largely from a political approach. For a long time, tax competition was perceived as something positive. Over the last fifteen years, following the setting of the European financial area, the economical crisis has led to increased concerns over loss of tax revenues, in particular revenues generated by mobile factors of production. This phenomenon underpinned the European initiative to regulate tax competition which was carried out especially through the Code of conduct on direct taxation of undertakings and the rules on State aid. The subject matter at issue is knowing why the Union, having for a long time applied the rules on State aid to taxation, needs, all of a sudden, a new political instrument providing roughly the same results? Which is, after all, the relationship between the Code of Conduct and the rules on State aid? An answer to this question entails the prior examination of these two instruments. Title II, "The code of conduct for business taxation: politics without law? ", is devoted to the genesis of the Code of conduct, in particular to the analysis of the contents of its preliminary works, nature and characteristics, the system of control of harmful tax measures, the geographical areas and tax measures covered by the Code, in particular the interpretation of identification and evaluation criteria of tax measures covered, the Primarolo Report and its follow-up, the Guidelines 2000 and the results of all this process. Title III, "The regulation of the State aid on taxation: law without politics?", is devoted to the critical analysis of the principles governing State aid (incompatibility, indifference of the goals and form.