The bulk transfer of electrical energy over long distances from generating stations to electrical substations through high voltage (at least 115 kilovolts (kV)) transmission lines. By contrast, the transport of electricity from substations to customers through low voltage lines (less than 34.5 kV) is known as electricity distribution. Lines that carry power at voltages between 34.5 kV and 115 kV may be classified as transmission or distribution lines depending on whether they move bulk power from power plants to different utilities or within a single utility to retail consumers. Electricity is generated at lower voltages and stepped up through transformers to match the voltage of the transmission lines before it enters the transmission network. This is because transmission lines can carry more power and will experience lower line losses. Transmission lines are generally subject to federal regulation and distribution lines are regulated under state law.

Although transmission is a key component of the electricity delivery system, it has been identified by the US Department of Energy, politicians, and energy industry experts as one of the key barriers to electricity generation in the US. This is because:

There are efforts underway at the same state and federal levels to promote and facilitate transmission development but significant work remains to allow many renewable energy projects to connect to the electric grid and deliver power. For more information on these challenges and efforts, see Article, Clean Energy: Key Developments and Trends in 2022 and Outlook for 2023 and Practice Note, Biden Administration Energy and Climate Change Policies and Regulations: 2023 Tracker : Transmission Regulations.

For more information on transmission lines more generally, see Practice Notes, Wind Energy Project Development Issues: Preliminary Considerations and Solar Energy Project Development Issues: Preliminary Considerations.