Initially, governments were intimately involved in the advancement of nuclear energy, owning the organisations developing the technology and sometimes those commercially exploiting it for power production. With the liberalisation of electricity markets and the privatisation of the generating assets in a number of countries, the pattern is now more mixed. Today, the structures of ownership vary considerably around the world, with liberalisation diluting government control and responsibility for the development and deployment of civil nuclear technology in several countries. However, all governments are facing one or more of the pressures of ensuring security of energy supply, rising fossil fuel prices and the need to constrain the emissions of greenhouse gases (GHGs). Regardless of the degree of control that individual governments have on the mix of generation sources in their electricity markets, many governments and political parties are re-evaluating the role that nuclear power could or should play.