The nation that will insist upon drawing a broad line of distinction between the fighting man and the thinking man is liable to find its fighting done by fools and its thinking by cowards.
-- Sir William Francis Butler
Government organizations have put substantial effort into detecting and thwarting terrorist and insurgent attacks by observing suspicious behaviors of individuals at transportation checkpoints and elsewhere. This report reviews the scientific literature relating to observable, individual-level behavioral indicators that might, along with other information, help detect potential violent attacks.