Chemical-Biological Warfare (CBW), warfare involving the use of chemical agents (other than explosives) and biological agents as weapons. In general, chemical agents of warfare are chemical substances (usually gases, but also liquids and solids) employed because of their poisonous effects on people, animals, and plants. Biological agents are harmful microorganisms (commonly called germs) and the toxins, or poisons, they produce.

CBW can be directed against an army, civilian population, or plant and animal life. The chemicals or biological agents can be spread over a limited area (with aerosol dispensers, hand grenades, or land mines, for example) or over a large area (as with artillery shells, bombs, aerial sprays, or missiles). It is all but impossible to devise adequate protection because gases and biological agents, once employed, are difficult to control and their effects are unpredictable.

The development, production, and use of chemical and biological agents have long been a source of concern and controversy. Proponents of CBW programs contend that such weapons furnish great offensive power at a relatively low cost. Tactically, these weapons provide a combat alternative to the use of conventional armaments and nuclear warheads. Moreover, supporters argue, such weapons are more humane than bullets and shells in that most CBW agents are intended to incapacitate rather than kill.

Opponents, on the other hand, contend that CBW agents are dangerously unreliable. Their use could result in countless human casualties and in long-term or even permanent damage to the balance of nature. One ounce (28 g) of botulism toxin, for example, could kill 60,000,000 people. Even if incapacitating rather than lethal agents were used initially, there would still be the risk of escalation to all-out chemical-biological warfare.