- all data concerning (1) design, manufacture, or utilization of atomic weapons; (2) the production of special nuclear material; or (3) the use of special nuclear material in the production of energy, but shall not include data declassified or removed from the Restricted Data category pursuant to section 142 [of the Act].
The concept was initially introduced, with similar wording, in the Atomic Energy Act of 1946. The fact that its legal definition includes "all data" except that already specifically declassified has been interpreted to mean that atomic energy information in the United States is born classified, even if it was not created by any agency of the U.S. government. The authority of the DOE to implement this authority as a form of prior restraint was only once tested in court, with inconclusive results.
Access to Restricted Data requires a Department of Energy Q clearance, which, As of 1993[update], requires a single-scope background investigation of the previous ten years of the applicant's life by both the Office of Personnel Management and the Federal Bureau of Investigation, and as of 1998[update] cost $3,225.
"Restricted Data" should not be confused with the classification category of "Restricted", a relatively low category of classification. "Restricted Data" is usually considered to be a Department of Energy equivalent of Top Secret or Secret. "Restricted Data" is not an exclusive form of classification; a document can be classified as containing "Restricted Data" and also be given a classification of "Top Secret", "Secret", or "Confidential".
Formerly Restricted Data is a category also designated in the Atomic Energy Act of 1954. Despite its name, it does not mean that the information so designated is unclassified. It means that they have been downgraded specifically for the purpose of sharing among military agencies as "National Security Information". It is defined as "Classified information which has been removed from the Restricted Data category after DOE and the Department of Defense have jointly determined that it relates primarily to the military utilization of atomic weapons, and can be adequately safeguarded as national security information."
See also 
- Atomic Energy Act of 1954, Chapter 2, Section 11(y).
- See 'United States v. The Progressive (1979).
- Alexander De Volpi, Jerry Marsh, Ted Postol, and George Stanford (1981). Born secret: the H-bomb, the Progressive case and national security. New York: Pergamon Press. ISBN 0-08-025995-2.
- William Burr, Thomas S. Blanton, and Stephen I. Schwartz, "The Costs and Consequences of Nuclear Secrecy" in Stephen I. Schwartz, ed., Atomic Audit: The Costs and Consequences of US Nuclear Weapons Since 1940 (Brookings Institution Press, 1998): 433-483; figures from Box 8-4, "Typical Costs of Security Investigations", on 461.
- U.S. Department of Energy, "An Overview of the Restricted Data and Formerly Restricted Data Classification System"