This research has developed a novel sustainability assessment framework for electricity technologies and scenarios, taking into account techno-economic, environmental and social aspects. The methodology uses a life cycle approach and considers relevant sustainability impacts along the supply chain. The framework is generic and applicable to a range of electricity technologies and scenarios. To test the methodology, sustainability assessments have been carried out first for different technologies and then for a range of possible future electricity scenarios for the UK. The electricity options considered either contribute significantly to the current UK electricity mix or will play a greater role in the future; these are nuclear power (PWR), natural gas (CCGT), wind (offshore), solar (residential PV) and coal power (subcritical pulverised). The results show that no one technology is superior and that certain tradeoffs must be made. For example, nuclear and offshore wind power have the lowest life cycle environmental impacts, except for freshwater eco-toxicity for which gas is the best option; coal and gas are the cheapest options, but both have high global warming potential; PV has relatively low global warming potential but high cost, ozone layer and resource depletion. Nuclear, wind and PV increase certain aspects of energy security but introduce potential grid management problems; nuclear also poses complex risk and intergenerational questions.Five potential future electricity mixes have also been examined within three overarching scenarios, spanning 2020 to 2070, and compared to the present-day UK grid. The scenarios have been guided by three different approaches to climate change: one future in which little action is taken to reduce CO2 emissions ('65%'), one in which electricity decarbonises by 80% by 2050 in line with the UK's CO2 reduction target ('80%'), and one in which electricity is virtually decarbonised (at the point of generation) by 2050, in line with current policy ('100%').In order to examine the sustainability implications of these scenarios, the assessment results from the present-day comparison were projected forward to describe each technology in future time periods. Additional data were compiled so that coal with carbon capture and storage (CCS) - a potentially key future technology - could be included. The results of the scenario analyses show that the cost of generating electricity is likely to increase and become more capital-intensive. However, the lower-carbon scenarios are also at least 87% less sensitive to fuel price volatility. Higher penetration of nuclear and renewables generally leads to better environmental performance and more employment, but creates unknown energy storage costs and, in the case of nuclear power and coal CCS, the production of long-lived waste places a burden of management and risk on future generations.Therefore, the choice of the 'most sustainable' electricity options now and in the future will depend crucially on the importance placed on different sustainability impacts; this should be acknowledged in future policy and decision making. A good compromise requires strategic government action; to provide guidance, specific recommendations are made for future government policy.