On March 28, 2017, President Trump signed an executive order to encourage and promote energy development by modifying climate change policies. As the Trump Administration implements its environmental policies, various legal challenges to Obama Administration climate change regulations remain pending before courts. During the last term of the Obama Administration, the Environmental Protection Agency (EPA) and the National Highway and Traffic Safety Administration finalized a series of regulations to address emissions from cars, trucks, and their engines that may contribute to climate change. In addition, EPA finalized regulations pursuant to its authority under the Clean Air Act (CAA) to reduce GHG emissions from stationary sources such as power plants, GHG-emitting oil and gas sources, and landfills. Various stakeholders have challenged a majority of these rules generally contesting the scope of EPA's authority and its methods for regulating GHG emissions. In addition to the CAA, other environmental statutes such as the Endangered Species Act and the National Environmental Policy Act require federal agencies to consider climate change in their actions and decisions. The extent to which agencies may consider climate change effects and rely on predictive models, studies, and assumptions, however, has been challenged in court. Federal agencies are also required to consider the cost of GHG emissions in their rulemakings and environmental reviews. As the Trump Administration implements its policies on climate change, stakeholders may sue to ensure compliance with laws and judicial precedent that require consideration of climate change effects or costs. Climate change litigation may potentially increase as some stakeholders seek to reduce GHG emissions and address climate change effects. In the past, plaintiffs have had little success in using federal common law nuisance claims to force private entities to reduce their GHG emissions or pay damages for alleged injuries caused by their emissions. In 2011, the Supreme Court determined that these claims were displaced when Congress granted EPA authority to regulate GHG emissions under the CAA. If Congress amends the CAA to remove EPA's authority, plaintiffs may seek to reintroduce these common law nuisance claims. However, they will likely face jurisdictional barriers that may be difficult to overcome. Federal courts often do not reach the merits of climate change suits due to threshold procedural and jurisdictional barriers, such as whether a plaintiff or petitioner has the right to bring a lawsuit in the first place or whether the court has jurisdiction over a type of claim. These difficult procedural and jurisdictional barriers are at the center of a recent case claiming that the government has a duty to safeguard certain natural resources for the benefit of the public and that duty compels the government to address climate change. This report will cover a brief history of U.S. climate change regulation; review the different types of regulation and legal actions that have been pursued in the national debate over GHGs; examine selected legal issues and next steps in related litigation; and address what these legal and regulatory developments mean for Congress.