<Table> <Tr> <Td> </Td> <Td> This article includes a list of references, but its sources remain unclear because it has insufficient inline citations . Please help to improve this article by introducing more precise citations . (August 2009) (Learn how and when to remove this template message) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This article includes a list of references, but its sources remain unclear because it has insufficient inline citations . Please help to improve this article by introducing more precise citations . (August 2009) (Learn how and when to remove this template message) </Td> </Tr> <P> In the United States, a security clearance is an official determination that an individual may access information classified by the United States Government . Security clearances are hierarchical; each level grants the holder access to information in that level and the levels below it . The clearance process requires a background investigation and the signing of a nondisclosure agreement . Access to any particular piece of information requires "need - to - know ." In some cases, this requirement is only nominal, as some classified information is widely published on secure networks . In other cases, there is a formal need - to - know determination . In addition to such a determination, Special Access Programs and Sensitive Compartmented Information may require additional investigation and adjudication of the prospective clearance holder . </P> <P> The authority for classifying information and granting security clearances to access that information is found in executive orders (EOs) and the USA's Federal law . USA's National Security Information (NSI) is classified under EO 13526 . Information may be classified under this Order if a classification authority determines its unauthorized release could cause damage to the national defense or foreign relations of the United States . Information concerning nuclear weapons and fissile material may be classified under the Atomic Energy Act of 1954 (AEA). These clearances are only granted by the Department of Energy . The clearance process for access to NSI or AEA information is substantially aligned . Under EO 12968, the investigative and adjudicative guidelines for NSI and AEA clearances are identical . This enables reciprocity between NSI and AEA clearances, although some exceptions exist . </P>

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