Decarbonizing the U.S. energy system will require a program of building onshore wind, offshore wind, utility-scale solar, and associated transmission that will exceed what has been done before in the United States by many times, every year out to 2050. These facilities, together with rooftop photovoltaics and other distributed generation, are required to replace most fossil fuel generation and to help furnish the added electricity that will be needed as many uses currently employing fossil fuels (especially passenger transportation and space and water heating) are electrified. This Article, excerpted from Michael B. Gerrard & John Dernbach, eds., Legal Pathways to Deep Decarbonization in the United States (ELI Press forthcoming 2018), discusses the four most important legal processes and obstacles involved in this enormous project: site acquisition and approval; the National Environmental Policy Act; state and local approvals; and species protection laws. It also presents recommendations for lowering the obstacles and briefly discusses several corollary actions that are needed.