Energy systems are changing rapidly around the world, with increasingly deep consequences for society, the economy, and geopolitics. These transitions demand a new approach to energy policy that extends beyond narrow considerations of technology and cost to encompass the broader societal dimensions of energy change. This talk introduces a new framework for energy policy analysis and implementation built around the concept of socio-energy system design. People literally inhabit energy systems, both existing and future, living, working, and playing amidst energy technologies and markets. Especially in the context of large-scale transitions, therefore, design choices for future energy systems will have significant consequences not only for how energy technologies work and generate business value but also for health and wellbeing, livelihoods, relationships, institutions, and political and economic power. Evidence is growing rapidly that the social dynamics of energy transitions are already feeding back (e.g., in the form of social movements, political opposition, or market choices) into energy industry choices. The challenge confronting new energy technologies is thus not simply scale but also social and economic geography—not just can we build a TW of solar PV or a GT of carbon storage, but which TW or GT will we build, how will the system and its socio-economic arrangements be designed, and with what distribution of costs, benefits, and risks for diverse communities.