1925 Geneva Protocol
Adopted in Geneva in 1925, the Protocol for the Prohibition of the Use in War of Asphyxiating, Poisonous or other Gases, and of Bacteriological Methods of Warfare was signed in Geneva on 17 June 1925 and it entered into force on 8 February 1928. As of 1 January 2008, 135 countries had ratified it.
This protocol refers to the use of chemical and biological weapons. Separate treaties deal with production and proliferation: the Chemical Weapons Convention and the Biological Weapons and Toxins Convention.
Arguably, its ancestry can be traced to the prohibition, in the Regulations Respecting the Laws and Customs of War on Land annexed to both the 1899 Hague Convention (II) with Respect to the Laws and Customs of War on Land and the 1907 Hague Convention (IV) Respecting the Laws and Customs of War on Land later codified this on polluting wells or poisoning bullets.