Anthrax weaponization is the development and deployment of the bacterium Bacillus anthracis or, more commonly, its spore (referred to as anthrax), as a biological weapon. As a biological weapon, anthrax has been used in biowarfare and bioterrorism since 1914. However, in 1975, the Biological Weapons Convention prohibited the "development, production and stockpiling" of biological weapons. It has since been used in bioterrorism.

Anthrax spores can cause infection from inhalation, skin contact, ingestion or injection and when untreated can lead to death. Likely delivery methods of weaponized anthrax include aerial dispersal or dispersal through livestock. Notable bioterrorism uses include the 2001 anthrax attacks and an incident in 1993 by the Aum Shinrikyo group in Japan.

Concentrated anthrax spores, and not necessarily the bacterium Bacillus anthracis, pose the biggest risk as a biological weapons to humans. When airborne, anthrax spores are not easily detectable, and are several microns in diameter. They are able to reach deep into the lungs when inhaled. Once the spores are in the lungs they are then able to replicate in blood, travel to the lymph nodes, and produce toxins which lead to death. Post exposure symptoms resemble flu-like illness followed by a fulminant phase of severe acute respiratory distress, shock and, ultimately death.

Anthrax spores are able to be dispersed via multiple methods and infect humans with ease. The symptoms present as a common cold or flu, and may take weeks before appearing. The destructive effects of an anthrax attack on a large city may have the destructive capacity of a nuclear weapon.

A mathematical model of a simulated large-scale airborne anthrax attack in a large city (1 kg anthrax spores in a city of 10 million people) was created, which takes into account the dispersion of spores, the age-dependent dose-response, the dynamics of disease progression and the timing and organization of medical intervention. The results of this model with the most efficient medical response resulted in more than 100000 deaths, which increases by a factor of 7 with slower antibiotic distribution.

Outside of the initial threat to individuals there are the costs of economic disruption, decontamination and treatment from such an event. The economic costs of the 2001 anthrax attacks resulted in over 100 million dollars being spent to decontaminate postal plants. The contamination is thought to have been less than 1 gram of anthrax spores in the facilities. The cost to decontaminate the Hart Senate Office Building after the 2001 anthrax attacks cost approximately 23 million dollars, with approximately 2 grams of anthrax spores present.

Detection of airborne anthrax requires 24–48 hours. Rapid detection in the atmosphere is not yet technologically effective. The system put in place on 22 January 2003 to assist in detecting an airborne anthrax attack by the United States is the U.S. Bio-watch Surveillance Network, which is able to detect airborne anthrax within 24–48 hours, however with some false positives and false negatives, leading to severe lag in detection and critical time lost for prevention and treatment.

Vaccination to anthrax is available, requiring 6 shots over an 18-month period and annual booster shots for full immunity. Vaccination of military personnel and first responders is vital to sustain a post attack response. The complete vaccination of an entire population can be achieved over a period of years, resulting in the reduction of risk from anthrax comparable to the reduction of risk of nuclear weapons by anti-ballistic missile systems.