The definition of what is of general interest is not a free and capricious decision of the legislator and the Administration. The most important public decisions must be preceded by the necessary information, and in particular, by methods and knowledge to weigh up and value the effects of planned measures, as well as possible alternatives or options. That is regulatory impact assessment. This book brings experiences of comparative law, notably France and the United States, both are advanced countries in this field, and offers reflections of interest to everyone, due to the techniques of regulatory impact assessment, embedded in modern administrative procedures are performed both state and supra-state level as in the major part of the world. The work includes the vision of a large group of international experts, in a clear and simple language, essential to get in a long-range and topical subject.