General Discussion
In reply to the discussion: I'm waiting a bit before forming a solid opinion on this NSA mess. [View all]jeff47
(26,549 posts)A classification is something applied to a thing. A document can receive a classification of Top Secret.
A person receives a security clearance. That allows that person to see things that have a classification. Someone with a Top Secret clearance can view a document with a Top Secret classification.
The instructions for what things are classified are in classification guides. The guides are published by the major entities that deal with classified information. For example, there's a DoD guide, from which Air Force, Army, Navy and Marine Corps guides are created.
Each derivative classifier (such as the Secretary of Defense and the Director of National Intelligence) sets up a program to investigate people for the purpose of granting security clearances. To again use the DoD example, DISA does security clearance investigations.
The Wikipedia entry on "Classified Information in the United States" and related articles are surprisingly detailed and thorough.