Public confidence in the security of the US food and fiber system has been sustained by the quality, variety, abundance, and affordability of agricultural products in the United States. Although the system in place to defend against unintentional threats to agriculture has weaknesses and needs, the demonstrated ability of the system to resolve, accommodate, or manage critical food safety problems, temporary shortages of some commodities, plant and animal infestations and diseases, and natural disasters indicates that, in general, such confidence has been warranted. However, over the last several years, there has been recognition of the possibility and consequences of intentional threats directed at US agriculture. Such attacks could come from foreign or domestic terrorists and use biological, chemical, or radiological agents. They could be directed at the pre harvest (live plant and live animal) or post harvest (processing and distribution) stages of food and fiber production.Countering Agricultural Bioterrorism asseses the vulnerability of US agriculture to intentional threats and provides recommendations needed to strengthen and adapt the US system for defense against biological threats to agriculture.