Energy law is not one field but a federation of them, and this UpLaw guide maps the whole territory: the constitutional and statutory division of authority that gives the Federal Energy Regulatory Commission the wholesale market and interstate transmission while leaving retail rates, generation siting, and resource choice to the states. It traces the Federal Power Act and Natural Gas Act "just and reasonable" standard from Hope and Bluefield through Mobile-Sierra and the filed rate doctrine, then walks the traditional rate case — rate base, rate of return, prudence review, and used-and-useful — before turning to the restructured world of RTOs, locational marginal pricing, capacity auctions, and the interconnection queue that now gates every new project in America. It explains PURPA and avoided cost, the anatomy of a renewable project from site control through offtake and tax equity, the federal tax credits that drive renewable economics and their new transferability, state renewable portfolio standards and the REC markets that implement them, oil-and-gas property law from the rule of capture to post-production cost splits, pipeline certificates and eminent domain after PennEast, the NEPA and Clean Water Act overlays that decide whether anything gets built, and the emerging law of storage, DER aggregation, and mandatory reliability standards. A running hypothetical — Windward Renewables, taking a solar-plus-storage project from a landowner option to financial close — grounds each doctrine. Retail ratemaking, siting, RPS design, and mineral property law are state law and vary enormously; the tax rules change with every Congress; verify current law before relying on anything here.