Chapter 5, “Conclusions”, was written by the project team. This is especially true for advanced industrial or post-industrial societies, where electricity provides the services essential for production, communication and exchange. Unsurprisingly, governments of OECD countries are thus concerned with understanding the factors influencing the security of energy and electricity supplies and seek to develop policy frameworks and strategies to enhance them. However, before proceeding towards the demonstration of the contribution of nuclear energy, the complex concept of “security of energy supply” must itself be defined and made amenable both to the formulation of concrete policy objectives and numerical verification.