The Freedom of Information Act (FOIA) (5 U.S.C. § 552) requires that Federal agencies make certain information available to the public-either affirmatively or upon request. Prior to the enactment of FOIA in 1966, except for those types of information either subject to discovery in litigation with the Government, or required by law to be made public, Federal agencies could arbitrarily decide what documents to release to the public and who could receive certain types of information. Now agencies are required to release copies of documents to any requester that do not fall into one of nine specifically exempt categories. These categories are:

1. Classified national defense or foreign policy documents.
2. Materials related solely to an agency's personnel rules and practices.
3. Materials specifically exempted from disclosure by statute.
4. Trade secrets and commercial or financial information obtained from a person and that is privileged or confidential.
5. Inter-agency or intra-agency memoranda or letters.
6. Personnel or medical files the disclosure of which would be an invasion of personal privacy.
7. Investigatory records compiled for law enforcement purposes.
8. Information concerning financial institutions.
9. Geological information concerning wells.

After receiving a written request for information under FOIA, an agency has 20 working days (subject to one extension) to either comply with the request or send a written denial specifically invoking one or more of the exemptions. The denial letter must also contain instructions for appealing the decision within the agency. If an agency also rejects the appeal, the requester has the option of taking the agency to court.

If parts of documents are deemed exempt from release, the agency must release the rest of the document where feasible. Agencies retain the discretion to release exempt documents in many situations. The Act also provides rules concerning fees that may be charged to requesters.

In 1996 the FOIA was updated by the Electronic Freedom of Information Act Amendments (Pub. Law 104-231).