The principal statute addressing air quality concerns, the Clean Air Act was first enacted in 1955, with major revisions in 1970, 1977, and 1990 and is addressed in the first part of this book. Congressional actions on air quality issues have been dominated since 2011 by efforts- particularly in the House-to change the Environmental Protection Agency's (EPA's) authority to promulgate or implement new emission control requirements. EPA's regulations on greenhouse gas emissions from electric power plants and from oil and gas industry sources have been of particular interest, as have the agency's efforts to revise ambient air quality standards for ozone. The 115th Congress and the Trump Administration are reviewing some of these regulations, with the possibility of their modification or repeal. On October 23, 2015, the U.S. Environmental Protection Agency (EPA) published its final Clean Power Plan rule (Rule) to regulate emissions of greenhouse gases (GHGs), specifically carbon dioxide (CO2), from existing fossil fuel-fired power plants. The aim of the Rule, according to EPA, is to help protect human health and the environment from the impacts of climate change. The Clean Power Plan would require states to submit plans to achieve state-specific CO2 goals reflecting emission performance rates or emission levels for predominantly coal- and gas-fired power plants, with a series of interim goals culminating in final goals by 2030.