Electricity supplies an increasing share of the world's total energy demand and that contribution is set to increase. At the same time, there is increasing socio-political will to mitigate impacts of climate change as well as to improve energy security. This, in combination with the desire to ensure social and economic prosperity, creates a pressing need to consider the sustainability implications of future electricity generation. However, approaches to sustainability assessment differ greatly in their scope and methodology as currently there is no standardised approach. With this in mind, this paper reviews sustainability indicators that have previously been used to assess energy options and proposes a new sustainability assessment methodology based on a life cycle approach. In total, 43 indicators are proposed, addressing the techno-economic, environmental and social sustainability issues associated with energy systems. The framework has been developed primarily to address concerns associated with nuclear power in the UK, but is applicable to other energy technologies as well as to other countries. © 2011.