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The Freedom of Information Act generally provides that any person has a right, enforceable in court, to obtain access to federal agency records, except to the extent that such records or portions thereof are protected from disclosure by one of nine exemptions or by one of three special law enforcement record exclusions.
Enacted in 1966, the FOIA established for the first time an effective statutory right of access to government information. The principles of government openness and accountability underlying the FOIA are inherent in the democratic ideal: "The basic purpose of FOIA is to ensure an informed citizenry, vital to the functioning of a democratic society, needed to check against corruption and to hold the governors accountable to the governed."
The Supreme Court emphasized that "official information that sheds light on an agency's performance of its statutory duties falls squarely within that statutory purpose." 
Exemption (b)(1) protects from disclosure national security information concerning the national defense or foreign policy, provided that it has been properly classified in accordance with Executive Order 13526.
Exemption (b)(2) exempts from mandatory disclosure records "related solely to the internal personnel rules and practices of an agency."
Exemption (b)(3) covers information "specifically exempted from disclosure by statute."
Exemption (b)(4) protects "trade secrets and commercial or financial information obtained from a person that is privileged or confidential."
Exemption (b)(5) protects "inter-agency or intra-agency memorandums or letters which would not be available by law to a party ... in litigation with the agency."
Exemption (b)(6) permits the government to withhold all information about individuals in "personnel and medical files and similar files" when the disclosure of such information "would constitute a clearly unwarranted invasion of personal privacy."
Exemption (b)(7)(A) authorizes the withholding of "records or information compiled for law enforcement purposes, but only to the extent that production of such law enforcement records or information ... could reasonably be expected to interfere with enforcement proceedings."
Exemption (b)(7)(B) protects "records or information compiled for law enforcement purposes (the disclosure of which) would deprive a person of a right to a fair trial or an impartial adjudication."
Exemption (b)(7)(C) provides protection for personal information in law enforcement records the disclosure of which "could reasonably be expected to constitute an unwarranted invasion of personal privacy."
Exemption (b)(7)(D) provides protection for "records or information compiled for law enforcement purposes which could reasonably be expected to disclose the identity of a confidential source and information furnished by a confidential source."
Exemption (b)(7)(E) provides protection to all law enforcement information which "would disclose techniques and procedures for law enforcement investigations or prosecutions, or would disclose guidelines for law enforcements investigations or prosecutions if such disclosure could reasonably be expected to risk circumvention of the law."
Exemption (b)(7)(F) permits the withholding of information necessary to protect the physical safety of "any individual" when disclosure of information about him "could reasonably be expected to endanger his life or physical safety."
Exemption (b)(8) protects matter that are "contained in or related to examination, operating, or condition reports prepared by, on behalf of, or for the use of an agency responsible for the regulation or supervision of financial institutions."
Exemption (b)(9) protects "geological and geophysical information an data, including maps, concerning wells."
The (c)(1) exclusion authorizes federal law enforcement agencies, under specified circumstances, to shield the very existence of records of ongoing investigations or proceedings by excluding them entirely from the FOIA's reach.
The (c)(2) exclusion provides that "whenever informant records maintained by a criminal law enforcement agency under an informant's name or personal identifier are requested by a third party, the agency may treat the records as not subject to the requirements of the FOIA unless the informant's status has been officially confirmed."
The (c)(3) exclusion pertains only to certain law enforcement records that are maintained by the Federal Bureau of Investigation.