A Single Scope Background Investigation (SSBI) is a type of security investigation conducted by the US Government to obtain a Top Secret (TS) clearance and access to Sensitive Compartmented Information (SCI). The Standard Form 86 (SF86) is required to begin the background check process. The background investigation includes:
- Checks of employment, education, organization affiliations, local agencies, where the subject has lived, worked, or gone to school
- Interviewing employers, coworkers and other individuals
- Interviewing friends and family members
- Four references are needed at a minimum
- Encompasses the past ten years or to age 18
- Citizenship verification
- The investigation may include a National Agency Checks with Local Agency Checks (NACLC) on the candidate’s spouse or cohabitant and any immediate family members who are U.S. citizens other than by birth or who are not U.S. citizens
- Credit check
- Public records check
There are three (3) main phases to receiving a security clearance:
- The first phase is the application process. This involves verification of U.S. citizenship, fingerprinting and completion of the Personnel Security Questionnaire (SF-86). The Electronic Questionnaires for Investigations Processing system (e-QIP) allows applicants to electronically enter, update, and transmit their personal investigative data over a secure Internet connection to their employing agency or security management office for review and approval of the personnel security investigation request.
- The second phase involves the actual investigation of your background. Most of the background check is conducted by the Defense Security Service (DSS).
- The final phase is the adjudication phase. The results from the investigative phase are reviewed. The information that has been gathered is evaluated based on thirteen factors determined by the Department of Defense (DoD). Some examples of areas they consider are; allegiance to the United States, criminal and personal conduct, and substance abuse or mental disorders. Clearance is granted or denied following this evaluation process.
Once the clearance is granted, the candidate is briefed on “the proper safeguarding of classified information and on the criminal, civil, and administrative sanctions that may be imposed on an individual who fails to protect classified information from unauthorized disclosure.” He or she is also required to sign an approved non-disclosure agreement (e.g., Form SF-312).
Investigations satisfying the scope and standards specified above are transferable between agencies and shall be deemed to meet the investigative standards for access to collateral Top Secret/National Security Information and Sensitive Compartmented Information (SCI). No further investigation or reinvestigation prior to revalidation every five years will be undertaken unless the agency has substantial information indicating that the transferring individual may not satisfy eligibility standards for clearance or the agency head determines in writing that to accept the investigation would not be in the national security interest of the United States. 
AcqLinks and References:
-  Website: Wikipedia – Single Scope Background Investigation
- Website: Defense Security Service (DSS)
- Website: Electronic Questionnaires for Investigations Processing system (e-QIP)