Unconventional warfare is warfare in a manner differing from that of conventional warfare; in many cases, such unconventional means have been deemed terrorism or war crimes. Unconventional warfare involves assassination, espionage, genocide, raiding, and terrorism, sometimes using biological weapons, chemical weapons, and/or nuclear weapons. When referring to only biological and chemical weapons, the term CB agents is used. Prior to World War I, the use of military aircraft was often seen as unconventional, and criminal.

See also: asymmetric warfare, low-intensity operations, terrorism, special forces, gladio