The National Environmental Policy Act (NEPA) is an essential piece of United States environmental law. Congress established the Council on Environmental Quality within the Executive Office of the President as part of the National Environmental Policy Act of 1969. The act regulates environmental impact by requiring that all private, public, and non-profit institutions uphold standards, procedure, and assurances as specified by the act. NEPA is a method for analysis and regulation used by all government and non government projects must go through. When a project is subjected to NEPA regulatory analysis, it is first determined if an environmental impact statement (EIS) is necessary.

An EIS is an analytical investigation that determines the extent if any a project will have on the environment and includes any recommendations for alternative actions. Additionally, if an EIS is necessary, the project may then qualify for a categorical exemption. Categorical exemptions (CEs) are issued when a project is considered exempt from EIS compliance. When a projects are approved for exemption from a detailed EIS analysis, a federal agency has determined that no significant environmental impact will result from the project. Categorical exclusions are an interesting and complex aspect of NEPA regulation as different agencies have different qualifiers for approving CEs. For example, the Department of Energy rarely issues CEs outside of specific cases that they have come across within their regulatory industry.

According to NEPA legislation, categorical exclusions can be a significant undertaking. However, overall the process is quite efficient and certainly effective in regulating environmental impact. The National Parks Service (NPS) issues categorical exemptions to its projects regularly. The NPS manages parks within the national parks system, such as Yosemite and Yellowstone National Parks. The agency has an open and publicly involved process for issuing CEs. This requires that the agency makes a diligent effort to involve any interested and affected public that exist. A complete guide to using the CEs list is available on the NPS website, including a list of questions asked most frequently. The guide also outlines exceptions for CEs and the process of obtaining a CE in greater detail.

Projects such as replacing older pipes, updating equipment, adding new features, and refurbishing buildings, typically receive CEs on regular basis. Although these are projects that are necessary to upkeep the aesthetic and safety quality of the park, they can also be disturbing to surrounding wildlife and habitat so it is important to assess the impact of these projects before moving forward. Once it is determined that minimal impact will occur, the project will likely receive a categorical exclusion under NEPA. Any business that is subject to NEPA regulations may apply for categorical exclusions for project proposals.