Research on sustainability transitions has expanded rapidly in the last ten years, diversified in terms of topics and geographical applications, and deepened with respect to theories and methods. This article provides an extensive review and an updated research agenda for the field, classified into nine main themes: understanding transitions; power, agency and politics; governing transitions; civil society, culture and social movements; businesses and industries; transitions in practice and everyday life; geography of transitions; ethical aspects; and methodologies. The review shows that the scope of sustainability transitions research has broadened and connections to established disciplines have grown stronger. At the same time, we see that the grand challenges related to sustainability remain unsolved, calling for continued efforts and an acceleration of ongoing transitions. Transition studies can play a key role in this regard by creating new perspectives, approaches and understanding and helping to move society in the direction of sustainability.

Prosumers are agents that both consume and produce electricity. With the growth in small and medium-sized agents using solar photovoltaic panels, smart meters, vehicle-to-grid electric automobiles, home batteries, and other "smart" devices, prosuming offers the potential for consumers and vehicle owners to revaluate their energy practices. As the number of prosumers increases, the electric utility sector of today will likely undergo significant changes over the coming decades, offering possibilities for greening of the system but also bringing with it many unknowns and risks that need to be identified and managed. To develop strategies for the future, policymakers and planners need knowledge of how prosumers could be integrated effectively and efficiently into competitive electricity markets. Here we identify and discuss three promising potential prosumer markets related to prosumer grid integration, peer-to-peer models, and prosumer community groups. We also caution against optimism by laying out a series of caveats and complexities.

Summary:The acceleration of low-carbon transitions across the sociotechnical systems of electricity, heat, buildings, manufacturing, and transport requires new conceptual approaches, analytical foci, and policy recommendations.Rapid and deep reductions in greenhouse gas emission are needed to avoid dangerous climate change. To provide a reasonable (66%) chance of limiting global temperature increases to below 2 o C, global energy-related carbon emissions must peak by 2020 and fall by more than 70% in the next 35 years.1 This implies a tripling of the annual rate of energy efficiency improvement, retrofitting the entire building stock, generating 95% of electricity from low-carbon sources by 2050 and shifting almost entirely towards electric cars.Deep decarbonization will necessitate low-carbon transitions across electricity, transport, heat, industrial, forestry and agricultural systems. But despite recent rapid growth in renewable electricity generation, the rate of progress towards this wider goal remains slow. Moreover, many energy and climate researchers remain wedded to disciplinary approaches that focus on a single piece of the lowcarbon transition puzzle. 2 A case in point is a recent Policy Forum 3 proposing a 'carbon law' that will guarantee that zero-emissions are reached. This model-based prescription focuses on policy, but not politics, culture, business, and social factors, thus avoiding many crucial real-world drivers of accelerated transitions.This Policy Forum presents a 'sociotechnical' framework that addresses the multidimensionality of the deep decarbonization challenge and shows how co-evolutionary interactions between technologies and multiple societal groups can accelerate low-carbon transitions. We organize this approach around four lessons, emphasizing factors that receive less attention in techno-economic and modeling approaches.