Biological warfare (or germ warfare) is when pathogens are used as a weapon. This is called a biological weapon. Pathogens are microorganisms that can cause disease. If non-living things (like toxins) are used, this is called chemical warfare.

Biological warfare has been used throughout history. The first form of biological warfare may have been when the plague hit the Mongols. During battle, they were said to have thrown plague victims' bodies at their enemies. Before the 20th century, it took some of the following forms:

• Deliberate poisoning of food or water supplies with infectious materials
• Use of microorganisms, living or dead animals in a weapon system.
• Use of fabrics that are contaminated