States have increasingly become linked through regional energy-related institutions, markets, infrastructure, and politics. ASEAN, EU, SADC, ECOWAS, Eurasian Union, NAFTA, and UNASUR, inter alia, have formal agreements and institutions covering energy. Renewable, nuclear, and fossil fuel energy sources, as well as pipelines and electricity grids, are all covered in the variety of regional formal and informal arrangements. In parallel, the scholarly body of literature on comparative regionalism is expanding, but generally without energy as a focus area. In a systematic review of eighty-six international relations and politics journals, this chapter finds fifty-two articles over a seventeen-year period linking regions and energy. While scholars are giving more attention to the empirics of energy regionalism, research now needs to turn to more systematic theory building along with comparisons between regions and across energy sources and infrastructure types. The chapter concludes with recommendations for a research agenda that focuses on three sets of questions about drivers, institutional design, and effects.