The security clearance process is designed to determine the trustworthiness of an individual prior to granting him or her access to classified national security information. The process has evolved since the early 1950s, with antecedents dating to World War II. This report highlights some of the fundamental aspects of the process by providing answers to frequently asked questions. A security clearance is a determination that an individual—whether a federal employee or a private contractor—is eligible for access to classified national security information. A security clearance may only be granted by a federal agency, and generally only upon completion of a background investigation. Using information obtained during the background investigation, the agency will make a determination as to the character and trustworthiness of the individual, and decide if he or she will be eligible for access to classified national security information. A security clearance alone does not grant an individual access to specific classified materials. Rather, a security clearance means that an individual is eligible for access. In order to gain access to specific classified materials, an individual should also have a demonstrated "need to know" the classified information for his or her position and policy area responsibilities. In addition, prior to accessing classified information, an individual must sign an appropriate nondisclosure agreement. A security clearance, as noted above, is designed to determine eligibility for access to classified information. A suitability check (or suitability determination), may involve many of the same investigative elements as a security clearance investigation. A suitability check, however, is designed to determine an individual's suitability for employment or appointment to certain federal positions. Unlike a security clearance, a suitability determination does not convey access to classified information. The levels of security clearances correspond to the levels of sensitivity of the information that cleared individuals will be eligible to access. The three levels, in ascending order, are Confidential, the unauthorized disclosure of which would "cause damage to the national security"; Secret, the unauthorized disclosure of which would "cause serious damage to the national security"; and Top Secret, the unauthorized disclosure of which would "cause exceptionally grave damage to the national security." In addition, there are two major categories of classified information that are commonly associated with the Top Secret level: Sensitive Compartmented Information (SCI), which refers to information involving intelligence sources and methods, and Special Access Programs (SAPs), which refers to highly sensitive policies, projects, and programs. These categories exist for classified information that has been deemed particularly vulnerable. Eligibility standards and investigative requirements for access to SCI and SAPs are higher than for other information classified at the same level, which further restricts the number of individuals that are eligible for access. An individual who is performing work for the federal government—whether that individual is a direct government employee or a private contractor—may be eligible to obtain a security clearance if his or her work requires access to classified materials. With certain limited exceptions, an individual must hold a security clearance in order to gain access to classified materials. Generally, only U.S. citizens are eligible to obtain a security clearance. Under Executive Order 12968, with limited exceptions, eligibility for access to classified information shall be granted only to employees who are United States citizens for whom an appropriate investigation has been completed and whose personal and professional history affirmatively indicates loyalty to the United States, strength of character, trustworthiness, honesty, reliability, discretion, and sound judgment, as well as freedom from conflicting allegiances and potential for coercion, and willingness and ability to abide by regulations governing the use, handling, and protection of classified information. An individual may not obtain or initiate a security clearance on his or her own. An individual seeking employment with the federal government, or who wishes to do work as a contractor for the government, may be interested in obtaining a security clearance on his or her own, believing that holding a security clearance may expedite the hiring process, or provide him or her with an advantage when competing for government contracts. Yet, only a sponsoring agency may initiate the security clearance process. According to the Office of Personnel Management (OPM), "clearances are based on investigations requested by Federal agencies, appropriate to specific positions and their duties. Until a person is offered such a position, the government will not request or pay for an investigation for a clearance." Security clearances are not mandated for the President, Vice President, Members of Congress, Supreme Court Justices, or other constitutional officers. The criteria for election or appointment to these positions are specified in the U.S. Constitution, and except by constitutional amendment, no additional criteria (e.g., holding a security clearance) may be required. Further, "by tradition and practice, United States officials who hold positions prescribed by the Constitution of the United States are deemed to meet the standards of trustworthiness for eligibility for access to classified information." Additionally, as Commander-in-Chief, the President has the authority to establish the standards for access to classified national security information. This authority is typically exercised through the issuance of executive orders. Executive Order 13467, which covers suitability checks and security clearances for federal employees, applicants, and contractors, includes a determination of which executive branch individuals are covered and which are exempted. 'Covered individual' means a person who performs work for or on behalf of the executive branch, or who seeks to perform work for or on behalf of the executive branch, but does not include: (i) the President or (except to the extent otherwise directed by the President) employees of the President under section 105 or 107 of title 3, United States Code; or (ii) the Vice President or (except to the extent otherwise directed by the Vice President) employees of the Vice President under section 106 of title 3 or annual legislative branch appropriations acts. Congressional staff and judicial staff are required to hold security clearances to gain access to classified information. The requirements are established, for the most part, by public laws, congressional rules, and judicial procedures. For example, the Rules of Procedure of the U.S. Foreign Intelligence Surveillance Court states that "each member of the Court's staff must possess security clearances at a level commensurate to the individual's responsibilities." Within Congress, the Office of House Security and the Office of Senate Security require that staff obtain the appropriate security clearances and sign nondisclosure agreements in order to be eligible for access to classified national security information. According to the Office of the Director of National Intelligence (ODNI), approximately 4.3 million individuals held security clearances (of any level) as of October 1, 2015. This includes 2,885,570 security clearances at the Confidential or Secret level and 1,363,483 security clearances at the Top Secret level. A total of 638,679 security clearances were approved during FY2015. This includes 408,262 clearances approved at the Confidential or Secret level and 230,417 at the Top Secret level. It is important to note that the number of security clearances approved in FY2015 includes initial clearances and renewals of existing clearances that were subject to reinvestigation in FY2015. For this reason, the number of clearances approved does not reflect the number of new clearances issued. Table 1 provides a breakdown of these figures by government and contractor employees. Although the security clearance process involves a number of stages, the key steps to obtaining and maintaining a security clearance are pre-investigation, investigation, adjudication, and reinvestigation. Pre-Investigation . During this phase, the agency makes a determination that an employee or contractor requires access to classified information for the completion of his or her duties. At the request of the sponsoring agency, the individual will submit his or her clearance application material (e.g., Standard Form SF86). Investigation . Using the information provided by the applicant in his or her clearance application materials, a background investigation of the applicant is conducted. The background investigation may vary in terms of content, cost, and length of time for completion depending, in part, on the level of clearance being sought. The National Background Investigations Bureau (NBIB) within OPM is responsible for overseeing the majority of personnel background investigations. Adjudication . Once the background investigation is complete, the application enters the adjudication phase. During this phase, a determination is made whether to grant the applicant a security clearance. Generally, this decision is made by the sponsoring agency and is based on the information obtained during the background investigation. Reinvestigation. Individuals who hold security clearances are subject to periodic reinvestigations. Previously, the maximum number of years that a security clearance remained valid was tied to the individual's clearance level. For example, reinvestigations for someone with a Confidential clearance, the least demanding, occurred at least once every 15 years; Secret, at least once every ten years; and Top Secret, at least once every five years. OPM and the Office of the Director of National Intelligence (ODNI), however, reduced the reinvestigation timeline to five years for all clearance holders, regardless of access level. Private contractors are subject to the same clearance procedures as direct government employees. As noted above, an individual may not obtain or initiate a security clearance on his or her own. The process to obtain a security clearance must be initiated by a sponsoring federal agency. The process differs slightly for an individual who is employed by a company that performs work under contract with the federal government. First, the contractor must determine whether the employee requires access to classified information in order to perform the duties of his or her position. The contractor must inform the sponsoring agency (i.e., the "customer" agency for whom the work is being performed) that the employee requires access to classified materials. The sponsoring agency will consider the request and then determine whether to initiate the security clearance process for the employee. Previously, the Office of Personnel Management, Federal Investigative Services (OPM-FIS) oversaw approximately 95% of all background investigations.