Catastrophic events often illustrate a nation's preparedness in anticipating and preventing the extreme consequences of an intentional malicious attack. When terrorists hijacked four commercial aircraft for use as guided missiles against the World Trade Center and the Pentagon on September 11, 2001, the world's population became aware of the human potential to inflict destruction and harm, and the vulnerability of transportation systems against preventing the occurrence of similar disasters. Through research, simulation, and system analysis, procedures may be formulated that limit or eradicate the possibility of future occurrences. Operations research encompasses the optimal allocation of resources subject to constraints, as well as providing techniques that evaluate the performance of security policies. This article provides a survey of operations research activities directed toward analyzing and enhancing the aviation security system, with the intent to be informative and motivate the continual improvement of our nation's transportation security.