[en] This publication first proposes texts of interventions in a meeting on the contribution of prospective approaches to energetic decision. The contributors discuss the perspective for a society without fossil energies, the future of nuclear energy in the 21. century, the issue of energy prospective, the prospective approach, the role of prospective as a support to decision making, and prospective applied to car and mobility. Two articles report the content of two round tables. The first one addressed the methods and results of energy prospective, and the second discussed whether the prospective approach answers the expectations of decision-makers. An article comments the content of a report by the French Court of Auditors (Cour des Comptes) on the production cost of nuclear energy which notably discusses how this production cost is assessed, highlights the maintenance costs and discusses the issue of extension of the exploitation duration beyond 40 years, the perspective of evolution of the production cost during the extension period, and the sensitivity to the evolutions of future expenses