The United States Department of Energy (DOE) is an executive department of the U.S. federal government that oversees U.S. national energy policy and energy production, the research and development of nuclear power, the military's nuclear weapons program, nuclear reactor production for the United States Navy, energy-related research, and energy conservation.

The DOE was created in 1977 in the aftermath of the 1973 oil crisis. It sponsors more physical science research than any other U.S. federal agency, the majority of which is conducted through its system of National Laboratories. The DOE also directs research in genomics, with the Human Genome Project originating from a DOE initiative.

The department is headed by the secretary of energy, who reports directly to the president of the United States and is a member of the Cabinet. The current secretary of energy is Chris Wright, who has served in the position since February 2025. The department's headquarters are in southwestern Washington, D.C., in the James V. Forrestal Building, with additional offices in Germantown, Maryland.

In 1942, during World War II, the United States started the Manhattan Project to develop the atomic bomb under the U.S. Army Corps of Engineers. After the war, in 1946, the Atomic Energy Commission (AEC) was created to control the future of the project. The Atomic Energy Act of 1946 also created the framework for the first National Laboratories. Among other nuclear projects, the AEC produced fabricated uranium fuel cores at locations such as Fernald Feed Materials Production Center in Cincinnati, Ohio. The Energy Reorganization Act of 1974 split the responsibilities of the AEC into the new Nuclear Regulatory Commission, which was charged with regulating the nuclear power industry, and the Energy Research and Development Administration, which was assigned to manage the nuclear weapon, naval reactor, and energy development programs.

The 1973 oil crisis called attention to the need to consolidate energy policy. In 1977, President Jimmy Carter signed into law the Department of Energy Organization Act, which established the Department of Energy. The new agency, which began operations on October 1, 1977, consolidated the Federal Energy Administration, the Energy Research and Development Administration, the Federal Power Commission, and programs of various other agencies. Former Secretary of Defense James Schlesinger, who served under Presidents Nixon and Ford during the Vietnam War, was appointed as the first secretary.

President Carter proposed the Department of Energy with the goal of promoting energy conservation and energy independence, and developing alternative sources of energy to reduce the use of fossil fuels. With international energy's future uncertain for America, Carter acted quickly to have the department come into action the first year of his presidency. This was an extremely important issue of the time as the oil crisis was causing shortages and inflation. With the Three Mile Island accident, Carter was able to intervene with the help of the department. Through the DOE, Carter was able to make changes within the Nuclear Regulatory Commission, including improving management and procedures, since nuclear energy and weapons are responsibilities of the department.

In December 1999, the FBI was investigating how China obtained plans for a specific nuclear device. Wen Ho Lee was accused of stealing nuclear secrets from Los Alamos National Laboratory for the People's Republic of China. Federal officials, including then-Energy Secretary Bill Richardson, publicly named Lee as a suspect before he was charged with a crime. The U.S. Congress held hearings to investigate the Department of Energy's handling of his case. Republican senators thought that an independent agency should be in charge of nuclear weapons and security issues, rather than the DOE. All but one of the 59 charges against Lee were eventually dropped because the investigation proved the plans the Chinese obtained could not have come from Lee. Lee filed suit and won a $1.6 million settlement against the federal government and news agencies.

In 2001, American Solar Challenge was sponsored by the DOE and the National Renewable Energy Laboratory. After the 2005 race, the DOE discontinued its sponsorship.