The project will extend the work of the Transition Pathways project, in which an innovative collaboration between engineers, social scientists and policy analysts developed and analysed a set of 'transition pathways' towards a UK low carbon electricity system. The pathways aimed to meet the UK's target of an 80% cut on 1990 levels of greenhouse gas emissions by 2050. The team developed and applied tools to analyse the technical feasibility, social acceptability and environmental and economic impacts of these pathways. The research built a sound platform from which to address the challenge of realising a low carbon transition. The aim of the new project is to explore what needs to be done to achieve a transition that successfully addresses the energy policy 'trilemma', i.e. the simultaneous delivery of low carbon, secure and affordable energy services. We focus on electricity, but in a context that includes the electrical provision of heat and transport, and key EU developments and policies. The project will inform thinking and decision-making about technological and behavioural developments, and the roles of key energy system 'actors', governance arrangements and regulations in a low carbon transition. The team will: 1. Analyse actors' choices and decisions in past, current and prospective developments in electricity supply and demand; 2. Analyse the social, behavioural and technical drivers and implications of electricity users' responses to incentives on the demand side and how to integrate these responses into electricity systems; 3. Undertake techno-economic modelling and energy and environmental assessments of the developments in electricity supply (including transmission and distribution networks) needed to meet this responsive demand. This research will inform decision-making by central and local government policy-makers, energy firms - both incumbents and new entrants, and civil society groups with an interest in energy policy. Following analysis by the Committee on Climate Change and in view of its commitments under national and European targets, the UK government is envisioning a rapid expansion of low-carbon electricity generation as a key means of moving towards a low carbon economy. However, this will require significant and interconnected changes in the patterns of energy service demands, market and regulatory frameworks and energy company business models, as well as technological innovation and deployment. This research aims to inform decision-making by: 1. investigating how the choices and interactions of actors and structural factors could contribute to the realisation of low carbon pathways, and what are likely to be key decision or branching points; 2. assessing the role of future demand responses, understanding the factors that drive energy demand and energy-using behaviour, and integrating this analysis within a whole-systems framework of electricity system development; 3. developing a set of interacting and complementary tools to analyse electricity network infrastructure investment and operational decisions, in order to model decisions to invest in the range of fossil and low carbon generation, taking into account market design and subsidy mechanisms; 4. appraising the energy and environmental performance of the technological mix, on a whole systems basis, analysing future economic costs, benefits, risks and returns, and uncertainties, and using economic models to explore wider social welfare, growth and employment impacts. These strands of research will be brought together to form a 'whole systems analysis' of the technical, environmental, economic, and social implications of alternative transition pathways to a UK low carbon electricity future.