The use of biological agents for military or terrorist objectives, with the aim of destroying or reducing the size of an enemy army, to assault a city, or another location, is what biological threats are all about. The most common definition of biological hazards is the mass killing of humans by microorganisms such as viruses, bacteria, or poisons. Herds of farm animals or microorganisms that cause crop plant diseases, such as some fungi, can also be considered biological hazards. Biological hazards are not a recent development. Numerous attempts to employ infectious microbes for military objectives have been documented in historical texts. Using the corpses of those who perished from the plague as disease carriers is one example. During the fourteenth-century Battle of Caffa, the Tatars sent to the invading Mongol army to cause an epidemic. They perished in large numbers, negotiated with Italians, and left their city. The British army’s “gifting” of blankets used by smallpox victims to Native Americans in North America is another instance of the deployment of biological threats in the eighteenth century. Native Americans who had never been exposed to this illness before were totally susceptible to it and perished in large numbers. Today, the Geneva Convention forbids the use, storage, and investigation of biological dangers. In spite of this, numerous nations have carried out or are currently carrying out covert studies. Large anthrax bacilli were thrown into the atmosphere at Sverdlovsk (Yekaterinburg, modern-day Russia) in 1972 due to an accident that claimed 66 lives. During Operation Desert Storm in 1990–1991 in Iraq, significant amounts of readily usable botulinum toxin were found, which is among the most lethal poisons known to man. This chapter offers an overview of the threat and historical use of biological threats, and it underscores the critical need for stringent international regulation and cooperation to prevent their development and deployment.