The use of biological agents is not new, but before the 20th century, biological warfare took three main forms:

deliberate poisoning of food and water with infectious material

use of microorganisms, toxins or animals, living or dead, in a weapon system

use of biologically inoculated fabrics

Biological warfare has been practiced repeatedly throughout history. During the 6th Century B.C., the Assyrians poisoned enemy wells with a fungus that would make the enemy delusional. In 184 BC, Hannibal of Carthage had clay pots filled with venomous snakes and instructed his soldiers to throw the pots onto the decks of Pergamene ships.

Historical accounts from medieval Europe detail the use of infected animal carcasses, by Mongols, Turks and other groups, to infect enemy water supplies. Prior to the bubonic plague epidemic known as the Black Death, Mongol and Turkish armies were reported to have catapulted diseased corpses into besieged cities.

During the Middle Ages, victims of the bubonic plague were used for biological attacks, often by flinging their corpses and excrement over castle walls using catapults. The last known incident of using plague corpses for biological warfare occurred in 1710, when Russian forces attacked the Swedes by flinging plague-infected corpses over the city walls of Reval (Tallinn).

The Native American population was decimated after contact with the Old World due to the introduction of many different fatal diseases. The British army at least once used smallpox as a weapon, when they gave contaminated blankets to the Lenape during Pontiac's War. It is suspected but not confirmed that biological warfare was used against the Indians at other times as well.

Native peoples in Aptos gave Spaniards gifts of freshly cut flowers wrapped in leaves of poison oak.

During the United States Civil War, General Sherman reported that Confederate forces shot farm animals in ponds upon which the Union depended for drinking water.

Use of such weapons was banned in international law by the Geneva Protocol of 1925. The 1972 Biological and Toxin Weapons Convention extended the ban to almost all production, storage and transport. However, the Soviet Union continued research and production of offensive biological weapons in a program called biopreparat, despite having signed the Biological and Toxin Weapons Convention. The United States was unaware of the program until Dr. Kanatjan Alibekov, the first deputy director of biopreparat defected in 1992. It is, however, believed that since the signing of the convention the number of countries capable of producing such weapons has increased.

During the Sino-Japanese War (1937-1945) and World War II, Unit 731 of the Imperial Japanese Army conducted human experimentation on thousands, mostly Chinese. In military campaigns, the Japanese army used biological weapons on Chinese soldiers and civilians. This employment was largely viewed as ineffective due to inefficient delivery systems. However, new information has surfaced within the last decade, which alleges a more active Japanese usage. For example, firsthand accounts testify the Japanese infected civilians through the distribution of plagued foodstuffs, such as dumplings and vegetables. There are also reports of contaminated water supplies. Such estimates report over 580,000 victims, largely due to plague and cholera outbreaks. In addition, repeated seasonal outbreaks after the conclusion of the war bring the death toll much higher.

In response to suspected biological weapons development in Germany and Japan, the United States, United Kingdom, and Canada initiated a BW development program in 1941 that resulted in the weaponization of anthrax, brucellosis, and botulinum toxin. The center for U.S. military BW research was Fort Detrick, Maryland. Some biological and chemical weapons research was also conducted at "Dugway Proving Grounds" in Utah. Research carried out in the United Kingdom during World War II left Gruinard island in Scotland contaminated with anthrax for the next 48 years.

When biological and chemical weapons become too old, they sometimes need to be disposed of. Many N.A.T.O nations use the U.S. chemical weapons disposal facility on the tiny Johnston Atoll located in the middle of the Pacific.

Considerable research on the topic was performed by the United States, the Soviet Union (see Biopreparat), and probably other major nations throughout the Cold War era, though it is generally believed that such weapons were never used. This view was challenged by China and North Korea, who accused the United States of large-scale field testing of biological weapons against them during the Korean War (1950-1953). Their accusation is substantiated by Stephen Endicott and Edward Hagerman in 'The United States and Biological Warfare: secrets of the early Cold War and Korea' (Bloomington, Indiana University Press, 1998). In 1972, the U.S. signed the Biological and Toxic Weapons Convention, which banned "development, production and stockpiling of microbes or their poisonous products except in amounts necessary for protective and peaceful research." By 1996, 137 countries had signed the treaty.

In 1986, the U.S. government spent US$42 million on research for developing defenses against infectious diseases and toxins, ten times more money than was spent in 1981. The money went to 24 U.S. universities in hopes of developing strains on anthrax, Rift Valley fever, Japanese encephalitis, tularemia, shigella, botulin, and Q fever. When the Biology Department at MIT voted to refuse Pentagon funds for biotech research, the Reagan administration forced it to reverse its decision by threatening to cut off other funds.

There have been reports that the United States Army has been developing weapons-grade anthrax spores at Dugway Proving Ground, a chemical and biological defense testing facility in Utah, since at least as early as 1992. Under the BWC, nations are permitted to develop small amounts of BW agents for the purpose of defensive research. The United States maintains a stated national policy of never using biological weapons under any circumstances since November 1969 President Nixon.

Today, several countries have or are developing biological warfare programmes. According to the U.S. Department of Defense, more than ten countries are suspected to have continuing biological warfare programs, including Russia, Israel, China, Iran, Libya, Syria and North Korea. Offensive programs in Iraq were disbanded after the first Gulf War.

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