Vol. 36, No. 6, November–December 2006, pp. 514–529 issn 0092-2102  eissn 1526-551X  06  3606  0514 inf orms ® doi 10.1287/inte.1060.0253 ©2006 INFORMS A Survey of Operations Research Models and Applications in Homeland Security P. Daniel Wright, Matthew J. Liberatore, Robert L. Nydick Department of Decision and Information Technologies, Villanova University, Villanova, Pennsylvania 19085 {daniel.wright@villanova.edu, matthew.liberatore@villanova.edu, robert.nydick@villanova.edu} Operationsresearchhashadalonganddistinguishedhistoryofworkinemergencypreparednessandresponse, airline security, transportation of hazardous materials, and threat and vulnerability analysis. Since the attacks of September 11, 2001 and the formation of the US Department of Homeland Security, these topics have been gathered under the broad umbrella of homeland security. In addition, other areas of OR applications in home- landsecurityareevolving,suchasborderandportsecurity,cybersecurity,andcriticalinfrastructureprotection. The opportunities for operations researchers to contribute to homeland security remain numerous. Keywords : government: agencies; planning: government, homeland security. History : This paper was refereed. S ince September 11, 2001, the term homeland secu- rity hasenteredthevernacularoftheUnitedStates and of countries around the world. In the US, it is definedas“aconcertednationalefforttopreventterrorist attackswithintheUnitedStates,reduceAmerica’svulner- abilitytoterrorism,andminimizethedamageandrecover from attacks that do occur” (Office of Homeland Secu- rity 2002, p. 2). Despite the recency of the term, for decades the operations research community has been exploring issues that we now classify under home- land security. As far back as 1960, OR researchers were working on such issues. At the seventh inter- national meeting of the Institute of Management Sci- ences (TIMS), Wood (1961) highlighted US vulnera- bility and potential responses to nuclear attack. He called on the OR community to develop techniques and programs to maintain freedom. Since that time, operations researchers have focused on such top- ics as emergency preparedness and response, airline security,hazardousmaterialtransportation,andcyber security. All of these areas are increasingly important to homeland security. While they have done much, operations researchers still have rich opportunities available. The US Department of Homeland Security (DHS), formed in October 2001, has a broad set of responsi- bilities that contribute to securing the homeland. To form it, the government reorganized several agencies and programs and evaluated its existing security efforts (National Commission on Terrorist Attacks upon the United States 2004). It put several existing agencies under one domain to unite their efforts to better protect the country. The department is orga- nized into five directorates: border and transportation security, emergency preparedness and response, sci- ence and technology, information analysis and infras- tructure protection, and management. Each direc- torate contains several agencies that were formerly housed in different departments of the federal gov- ernment. For instance, the border and transportation security directorate now includes the US Customs Service, the Transportation Security Administration, and the Animal and Plant Health Inspection Service, which were originally the responsibility of the Trea- sury, Justice, and Agriculture Departments, respec- tively. For all of its directorates, the Department of Homeland Security states its mission as follows: We will lead the unified national effort to secure Amer- ica. We will prevent and deter terrorist attacks and protect againstandrespondtothreatsandhazardstothenation.We will ensure safe and secure borders, welcome lawful immi- grants and visitors, and promote the free-flow of commerce (Department of Homeland Security 2005). The mission is reinforced by several strategic goals, includingawareness,prevention,protection,response, 514