System innovations are long-term transitions from one sociotechnical system to another. They involve not only changes in technology, but also changes in user practices, regulation, industrial networks, infrastructure, and culture. Current scenario methods are not entirely suited to explore possible system innovations. They lack attention to the co-evolution of technology and society, and to insights from innovation studies and sociology of technology. Hence, we propose a new tool: sociotechnical scenarios. We illustrate the tool with two scenarios in the electricity domain, sketching transition paths to more sustainable systems. We also derive strategic policy recommendations from the two scenarios.Key words: co-evolution; sociotechnical scenarios; methodology; system innovation; electricity; strategic policy making.