In the US, while conducting your job search, you may come across job descriptions with the statement Secret clearance required or TS-SCI required. This means that the successful candidate must either already possess the appropriate level of security clearance or they must submit to and successfully complete a personnel security investigation (PSI). NOTE: Only citizens of the US are eligible to receive DoD Security Clearances. What then is a security clearance? There are two basic types of security clearances as relates to private (non-government) entities within the US. - Individual Security Clearances (applies to private citizens) - Facility Security Clearances (applies to business entities) In the US Department of Defense and other civilian Federal Agencies, all classified information falls into one of the following categories: CONFIDENTIAL: Applied to information or material which if disclosed to unauthorized personnel could potentially cause damage to the national security. SECRET: Applied to information or material which if disclosed to unauthorized personnel could potentially cause serious damage to the national security. TOP SECRET: Applied to information or material which if disclosed to unauthorized personnel could potentially cause grave or catastrophic damage to the national security. In addition to the above, some classified information is so sensitive that even the extra protective measures applied to Top Secret information are not sufficient. This information is known as "Sensitive Compartmented Information" (SCI) or Special Access Programs (SAP). Any individual needs special "SCI Access" or SAP approval to access to this information. An important item to note here is that "For Official Use Only" is not a security classification. It is used to protect proprietary information covered under the Privacy Act and does not relate to National Security. Any individual that requires access to classified information to perform his or her job functions requires the corresponding security clearance. If your job requires you to have access to CONFIDENTIAL information, you would require a CONFIDENTIAL Security Clearance. If your job requires you to have access to SECRET information, you would require a SECRET Security Clearance and so on.