Biological weapons introduce a bacteria or virus, combined with a delivery mechanism, into an environment for hostile purposes. Such agents can be very effective at killing plants, livestock, pets, and humans. 

Contemporary concerns about biological weapons do not simply involve possession or non-possession of weapons. Instead, concerns primarily involve the degree to which states have the capacity and intent to threaten or perpetrate a biological attack, a concern that is particularly relevant when it comes to countries’ biodefense programmes. Any state with a reasonably advanced pharmaceutical and medical industry has the capability of mass producing biological weapons. This fact also leads to problems with determining what countries have biological weapon programmes. Anything from a piece of fruit to a ballistic missile could be used to deliver a biological weapon to a target. Along with this is the fact that with certain organisms, only a few particles would be needed to start an infection that could potentially cause an epidemic. 

The Biological and Toxic Weapons Convention (BWC or BTWC) is the first multilateral disarmament treaty banning an entire category of weapons of mass destruction. It entered into force in March 1975. The Convention bans the development, production, stockpiling, and acquisition of biological agents or toxins of any type or quantity that do not have protective, medical, or other peaceful purposes, or any weapons or means of delivery for such agents or toxins. Under the treaty, all such materiel is to be destroyed within nine months of the Treaty's entry into force.

About 70 different chemicals have been used or stockpiled as chemical weapon agents during the 20th and 21st century. These chemicals are in liquid, gas, or solid form and blister, choke, and affect the nerves or blood. Chemical warfare agents are generally classified according to their effect on the organism and can be roughly grouped as: Nerve Agents, Mustard Agents, Hydrogen Cyanide, Tear Gases, Arsines, Psychotomimetic Agents, Toxins, and Potential CW Agents.

The Chemical Weapons Convention (CWC) bans the development, production, stockpiling, acquisition, transfer and use of chemical weapons by its states parties. The Treaty contains an extensive list of banned chemicals and precursors and provides for an elaborate and intrusive verification regime, through the Organisation for the Prohibition of Chemical Weapons (OPCW). The CWC opened for signature in 1993 and entered into force in April 1997. 

Unfortunately, since 2012 the long-standing norm against chemical weapons has been eroded by their use in Syria, Malaysia, and against Russian opposition leaders. This has led to widespread condemnation and outcry, while efforts toward investigation, attribution, and accountability for chemical weapons have been politically divisive, whether at the OPCW, the UN Security Council, or in the UN General Assembly.