Regulatory Impact Assessment (RIA) is a procedure used within the European Union (EU) since 2002. This procedural tool helps the institutions of the EU, at the centre of which the European Commission, in the preparation of every important decision at the EU level. During the RIA, institutional actors try to identify different possible political options, and to assess their economical, environmental, and social impacts. It is then formalized as a Report, which is annexed to the formal normative proposition.The European Union is a political space where normative decisions are taken. The actors, acts, and procedures involved in decision-making are partially identified and organized by Law. The elaboration of the norms is a part of its life-cycle. Therefore, it shall be considered by Law. The introduction of a Regulatory Impact Assessment procedure in the European Union improved the procedural dimension of the pre decisional phase. Regulatory Impact Assessment is an administrative tool aiming at helping the decision-maker in a pluricentric political space. It finds it roots in the global paradigm of “Better Regulation”. Its theoretical rationale is well identified and systematized with the help of the Theory of Rational Choice. Nowadays, RIA is considered as a “must have” in every legal system. However, it is also well proved that, in order to constitute a success story, the tool used must be adequate to the political system in which it is introduced. Is it the case within the European Union? This is what this book seeks to assess. It thus details, analyzes, and criticizes the juridical questions raised by the introduction and use of RIA within the EU institutional equilibrium.In the first part of this book, the author circumcises the different forms of contemporary normative activities in the EU. He then gives special attention to the pre decisional stage of decision making. RIA indeed has, even if not exclusively, an ex ante temporal dimension. This being done, the author justifies the introduction of an Impact Assessment procedure within the institutional framework of the EU.In the second part of his study, the author characterizes the practice of RIA within the EU, with the help of two practical examples. He then delimits the field of application of RIA, as well as its procedural details. At the end of this updated definition work, the reader is aware of what RIA should be, and what it is in the practical reality of EU’s institutional framework. He can also fully weigh the juridical problematic rose by the use of this procedural tool in the decision making process.It thus allows, in the third part of the book, to assess the interactions of Regulatory Impact Assessment with EU Administrative Law. The author deducts the legal consequences of the use of RIA on the decision making model of the European Union, and on the discretionary powers of the European Commission in the proposition phase. He also assesses the adequacy of the administrative model proposed by RIA with Better Regulation and Good Governance principles. He finally raises some criticisms on the administrative model proned by the European Commission, and defines the limited ability of RIA to enhance procedural legitimization of EU normative activities.