A fter the terrorist attacks of September 11, 2001, the federal government developed a unified regimen to identify and list known or suspected terrorists. The regimen has received repeated congressional attention, and this report briefly discusses for congressional policymakers how the U.S. government fashions and uses the Terrorist Screening Database (TSDB) to achieve such an end. It also discusses how the federal government engages in two travel-related screening processes—visa screening and air passenger screening. Both processes involve subsets of the Terrorist Screening Database. The TSDB as well as terrorist watchlisting and screening efforts are of keen congressional interest . This r eport endeavors to offer policy makers an overview of these issues to help in the development of policy and oversight . The material herein is drawn from publicly avail able information release d by federal agencies as well as other open source material. The report does not evaluate the TSDB or federal programs designed to prevent terrorist travel . The Terrorist Screening Database (TSDB, commonly referred to as the terrorist watchlist) lies at the heart of federal efforts to collect and share information with U.S. law enforcement and security agencies about identified people who may pose terrorism-related threats to the United States. It is managed by the Terrorist Screening Center (TSC) and includes biographic identifiers for those known either to have or be suspected of having ties to terrorism. In some instances it also includes biometric information on such people. It stores hundreds of thousands of unique identities. Portions of the TSDB are exported to data systems in federal agencies that perform screening activities such as background checks, reviewing the records of passport and visa applicants, and official encounters with travelers at U.S. border crossings. The TSC, a multi-agency organization administered by the Federal Bureau of Investigation (FBI), maintains the TSDB. The TSC was created by presidential directive in 2003 in response to the terrorist attacks of September 11, 2001. Before the TSC consolidated federal watchlisting efforts, numerous separate watchlists were maintained by different federal agencies. The information in these lists was not necessarily shared or compared. The efforts that surround the federal watchlisting regimen can be divided into three broad processes centered on the TSDB: Nomination, which involves the identification of known or suspected terrorists via intelligence collection or law enforcement investigations. The U.S. government has a formal watchlist nomination process. Verification of identities for the TSDB and export of data to screening systems, which involves managing records in the TSDB, as well as the compiling and export of special TSDB subsets for various intelligence or law enforcement end users (screeners). Screening, which involves end users—screeners—checking individuals or identities they encounter against information from the TSDB that is exported to screening databases. These databases include the No Fly List and the Selectee and Expanded Selectee lists for airline passenger screening; the Department of State's Consular Lookout and Support System (CLASS); the FBI's National Crime Information Center (NCIC); the TECS (not an acronym) system for border and port of entry screening; and the military base access and screening system. (In FY2011, there were "more than 1.2 billion queries against [the TSDB].") The screening and vetting processes can yield more information on particular subjects that may be fed back into the TSDB. (See Figure 1 for a visual depiction of the federal agencies involved in watchlisting.) The first step toward adding identities to the TSDB is the nomination process. In their daily work poring over raw information or case files, staff at U.S. government agencies—dubbed "originators" in the watchlisting process—uncover the possible identities of people suspected of involvement in terrorist activity. Such identities can be nominated for addition to the TSDB. Originators can work in places such as intelligence and law enforcement agencies or U.S embassies and consulates. The nominations they initiate include people who are classed together in the watchlisting regimen as "known or suspected terrorists" (KSTs). For the federal government's watchlisting regimen, a "known terrorist" is an individual whom the U.S. government knows is engaged, has been engaged, or who intends to engage in terrorism and/or terrorist activity, including an individual (a) who has been charged, arrested, indicted, or convicted for a crime related to terrorism by U.S. government or foreign government authorities; or (b) identified as a terrorist or member of a designated foreign terrorist organization pursuant to statute, Executive Order, or international legal obligation pursuant to a United Nations Security Council Resolution. A "suspected terrorist" is an individual who is reasonably suspected to be, or has been, engaged in conduct constituting, in preparation for, in aid of, or related to terrorism and/or terrorist activities based on an articulable and reasonable suspicion. All nominated identities of known or suspected terrorists for the TSDB are vetted by analysts at either the National Counterterrorism Center (NCTC) or the FBI and then undergo verification at the TSC. NCTC handles the nominations of all known or suspected international terrorists (including purely international suspects submitted by the FBI). In this process, NCTC maintains a classified database known as the Terrorist Identities Datamart Environment (TIDE). TIDE is the U.S. government's "central repository of information on international terrorist identities." TIDE includes: to the extent permitted by law, all information the [U.S. government] possesses related to the identities of individuals known or appropriately suspected to be or to have been involved in activities constituting, in preparation for, in aid of, or related to terrorism (with the exception of purely domestic terrorism information). In late 2013, TIDE contained the identities of approximately 1.1 million people. Of this number, about 25,000 were U.S. citizens and lawful permanent residents linked to international terrorist organizations. Not all of the entries in TIDE get into the TSDB, which according to the FBI held approximately 800,000 identities in November 2014. NCTC analysts constantly work on updating identities in TIDE, and NCTC exports a subset of its TIDE data holdings for the TSDB. TSC analysts perform a final verification of identities before they become a part of the TSDB. (For more about the concepts involved, see " Making the TSDB Cut .") TIDE is also an important resource on its own, used by counterterrorism professionals throughout the U.S. intelligence community in daily counterterrorism analytical work. FBI analysts in its Terrorist Review and Examination Unit process FBI nominations to the TSDB. These nominations often spring from FBI investigative work. The unit forwards international nominations to NCTC for inclusion in TIDE, where the data in the nomination is reviewed before release to the TSC. The FBI also forwards nominations of purely domestic terrorists and "domestic terrorists that may have connections to international terrorism" directly to the TSC for review. To make it into the TSDB, a nomination vetted by either NCTC or the FBI has to (1) meet the "reasonable suspicion watchlisting standard" and (2) have sufficient identifiers. TSC personnel verify that each nomination that makes it into the TSDB meets both of these criteria. The TSDB is a sensitive but unclassified dataset, and each record created by TSC personnel for the TSDB includes only an individual's identifiers and no "substantive derogatory information or classified national security" material. Articulable facts form the building blocks of the reasonable suspicion standard undergirding the nomination of suspected terrorists. Sometimes the facts involved in identifying an individual as a possible terrorist are not enough on their own to develop a solid foundation for a nomination. In such cases, investigators and intelligence analysts make rational inferences regarding potential nominees. The TSC vets all nominations, and when it concludes that the facts, bound with rational inferences, hold together to form a reasonable determination that the person is suspected of having ties to terrorist activity, the person is included in the TSDB. In the nomination process, guesses or hunches alone are not supposed to lead to reasonable suspicion. Likewise, one is not supposed to be designated a known or suspected terrorist based solely on activity protected by the First Amendment or race, ethnicity, national origin, and religious affiliation. Once the reasonable suspicion standard is met, analysts must have the ability to distinguish a specific terrorist's identity from others. Thus, minimum biographic crite ria must exist. At the very least, for inclusion in the TSDB a record must have a last name "and at least one additional piece of identifying information (for example a first name or date of birth)." Most nominations appear to make the TSDB cut. From FY2009 to FY2013, approximately 1.6 million individuals were nominated and only about 1% (just over 14,000) were rejected. (See Figure 2 .) The TSC routinely exports watchlist information to federal agencies authorized to conduct terrorist screening. According to the TSC, this occurs as the information is processed: "seconds later, it shows up with our partners so they can do near-real-time screening." According to the TSC, those partners consist of "five major U.S. Government agencies" that receive TSDB exports, which are subsets of the entire watchlist. Each of the agencies gets a different portion of the TSDB that is "tailored to [its] mission, legal authorities, and information technology requirements." Among the agencies whose screening systems make use of TSDB information are the following: The Department of State 's (DOS's) consular officers draw on TSDB information in the Consular Lookout and Support System (CLASS) used for passport and visa screening.