On April 19, 2018, the Federal Energy Regulatory Commission (FERC, or the commission) initiated a proceeding to review its policies and procedures for the certification (permitting) of interstate natural gas pipelines. Rapid expansion of the U.S. natural gas pipeline network to accommodate new supplies of domestic shale gas has been a focus of Congress, prompting hearings and legislative proposals over the last decade regarding the federal role in pipeline siting. Nine related bills have been introduced in the 115 th Congress, including the Promoting Interagency Coordination for Review of Natural Gas Pipelines Act ( H.R. 2910 ), which passed in the House in July 2017, and provisions in the Energy and Natural Resources Act of 2017 ( S. 1460 ). FERC's review of its permitting policies is the most recent development in an ongoing series of legislative proposals, executive orders, court rulings, and commission orders which address the federal role in gas pipeline permitting. FERC's review provides both advocates and opponents of gas pipeline development a new opportunity to express their views about how the commission considers such projects. It may also identify issues of focus for future congressional oversight and legislation. Given that the United States is the world's largest producer of natural gas, policy changes by FERC affecting natural gas infrastructure could have significant implications for U.S. natural gas resource development, prices, and associated environmental impacts. Therefore, they would likely be subject to scrutiny within Congress and among a wide range of stakeholders. This report provides an overview of the federal certification process for interstate natural gas pipelines and current policy challenges which have been the subject of debate and litigation. It reviews recent executive orders intended to facilitate or expedite federal approval of natural gas pipeline projects. The report summarizes legislation proposed since the 111 th Congress intended to change the federal review of interstate natural gas pipeline certificate applications. It also summarizes FERC's examination of its policy statement for natural gas pipeline certification, which serves as the basis of its review of pipeline certificate applications. The report concludes with a discussion of policy issues for Congress. The United States' supply of natural gas is growing due to technological improvements, such as horizontal drilling and hydraulic fracturing, which have increased producers' ability to extract natural gas from shale formations. Shale gas is projected to become the dominant source of the U.S. natural gas supply by 2030. The growth in U.S. shale gas production is driving the expansion of natural gas pipeline infrastructure at the local level (to gather and process the gas) and at the national level to transport natural gas from producing regions to consuming markets, typically in other states. Over 300,000 miles of high-capacity transmission pipeline already transport natural gas across the United States ( Figure 1 ). However, if the growth in U.S. shale gas continues as projected, the need for new pipelines could be substantial. One recent analysis by the INGAA Foundation, a pipeline industry research organization, projected the need for approximately 26,000 miles (1,400 miles annually) of new natural gas transmission pipeline between 2018 and 2035; total capital expenditure for these projects could range from $154 billion to $190 billion. Figure 2 shows annual additions to natural gas transmission pipeline mileage in the United States since 2004. As the figure indicates, federal and state agencies have approved significant additions to the pipeline system over the last 15 years, especially after the onset of the shale gas expansion in 2006-2008. Pipeline construction slowed for a five-year period through 2016 as newly added capacity absorbed new shale gas supplies, but construction has since increased. Altogether, over 24,000 miles of gas transmission pipeline have been constructed since 2004 or are anticipated for construction. Additional gas pipeline capacity has also become available through conversion of pipelines carrying other commodities or flow reversal of existing natural gas pipelines. Under Section 7(c) of the Natural Gas Act of 1938 (NGA), FERC is authorized to issue certificates of "public convenience and necessity" for "the construction or extension of any facilities ... for the transportation in interstate commerce of natural gas" (15 U.S.C. §717f(c)). Therefore, companies seeking to build interstate natural gas pipelines must first obtain certificates of public convenience and necessity from FERC. The commission's regulatory process for the review of certificate applications consists of several principal steps, explained below, which may vary somewhat depending upon whether or not a pipeline developer opts to enter into a voluntary pre-filing process before formally applying for a pipeline certificate. Prior to applying to FERC for a pipeline certificate, developers may file a request to use the commission's pre-filing procedures (18 C.F.R. §157.21). The commission established the pre-filing process to encourage the industry to engage early in project development with the relevant public and government agencies. The expectation is that the pre-filing will improve a developer's proposal and avoid problems during the review of a subsequent FERC certificate application. However, while FERC encourages pre-filing, it is not required to apply for a pipeline certificate. The pre-filing process involves a set of specific activities by the developer—typically studying potential project sites, identifying stakeholders, and holding an open house to discuss the project. Through this process, a developer notifies all stakeholders—including tribal, state, local, and other federal agencies, and potentially affected property owners—about a proposed project so that the developer and commission staff can provide public forums to hear stakeholder concerns. The pipeline developer may then incorporate proposed environmental mitigation measures into the project design, taking into account stakeholder input. Concurrent with the developer's activities, FERC staff participate in public forums and take steps necessary to ensure FERC compliance with the National Environmental Policy Act (NEPA, discussed below). For example, FERC consults with interested stakeholders, including relevant government agencies, and also holds public scoping meetings and site visits in the proposed project area. At the conclusion of pre-filing, the developer prepares a final application and submits it to FERC. Whether pre-filing or not, a pipeline developer must formally apply to FERC for a certificate of public convenience and necessity. Among other requirements, the application must contain a description of the proposed pipeline, route maps, construction plans, schedules, and a list of other statutory and regulatory requirements, such as permits needed from other agencies. The application must also include environmental reports analyzing route alternatives—to avoid or minimize environmental damage—and studies of potential environmental impacts (on water, plants, and wildlife), cultural resources, socioeconomics, soils, geology, aesthetic resources, and land use. Upon receiving an application, the commission issues a public Notice of Application in the Federal Register and begins the application review process. Any person seeking to become a party to FERC's proceeding must file a motion to intervene pursuant to the commission's rules (18 C.F.R. §385.214). Intervenors receive the certificate applicant's filings and other FERC documents related to the case, as well as materials filed by other interested parties. Only intervenors have the right to file briefs, attend hearings, and appeal the commission's decision regarding the certificate. They may also challenge final commission actions in the U.S. Circuit Courts of Appeal. FERC currently exercises its NGA Section 7(c) pipeline certification authority in accordance with its own regulations and the guidance of its 1999 Policy Statement on Certification of New Interstate Natural Gas Pipeline Facilities . The statement lays out FERC's "policy for determining whether there is a need for a specific project and whether, on balance, the project will serve the public interest." It also outlines a "flexible balancing process" within which the commission considers market support; economic, operational, and competitive benefits; and environmental impact, among other considerations. Economic factors FERC examines include a project's potential impact on pipeline competition, the possibility of overbuilding, subsidization by existing customers, acquiring rights-of-way (including the use of eminent domain), and other considerations. FERC may also take into account safety issues, but generally defers to the Department of Transportation, which regulates pipeline safety. Of the factors above, environmental review typically comprises the bulk of FERC's certificate application review. Before FERC can issue a final decision on an application, the agency must identify and consider the environmental impacts of the proposed project in accordance with NEPA (42 U.S.C. §4321 et seq.). NEPA requires federal agencies to consider the potential environmental impacts of actions it may approve (e.g., granting a certificate) and to inform the public about them before making a final decision. NEPA requires federal agencies to provide an environmental impact statement (EIS) for federal actions "significantly affecting the quality of the human environment." The Council on Environmental Quality (CEQ) promulgated regulations implementing NEPA that are broadly applicable to all federal agencies. In those regulations, CEQ directed each federal agency to adopt and supplement the CEQ regulations as necessary to include procedures relevant to that agency's authority and ensure that the procedures implementing NEPA are integrated into the agency's broader decisionmaking process. FERC subsequently did so when it promulgated its own regulations implementing NEPA (18 C.F.R. §380). The CEQ regulations focus primarily on requirements applicable to the preparation of an EIS, but recognize that documenting compliance with NEPA may involve other procedures. If an agency is uncertain whether a proposal would have significant impacts, it may prepare an environmental assessment (EA) to determine if an EIS is necessary or a finding of no significant impact (FONSI) may be issued. Also, each federal agency is required to identify categories of actions they are authorized to undertake that have been found to have no significant effect on the environment. Such actions are categorically excluded from the need to prepare an EIS or EA and are, hence, broadly referred to as "categorical exclusions" (CEs or CATEXs).