In recent decades, our lifestyle and growing wealth has had a profound effect on the energy sector, changing the energy outlook considerably in the process. Increasing demand for energy, soaring oil prices, uncertain energy supplies and fears of global warming have opened our eyes to the fact that plentiful energy can no longer be taken for granted. Different EU policy developments and national energy strategies have stressed that the choice of the energy mix – fossil, renewable or nuclear – remains at the national level. However, it is generally accepted that in order to ensure the security of supply member states are obliged to consider a suitably diversified energy portfolio in terms of a resource and technology mix and of import and transit routes and means. In addition, there is a definite need for solidarity between the member states when facing problems of the security of supply, as included in the Revised Treaty.