The modern use of chemical weapons began with World War I, when both sides to the conflict used poisonous gas to inflict agonizing suffering and to cause significant battlefield casualties. Such weapons basically consisted of well known commercial chemicals put into standard munitions such as grenades and artillery shells. Chlorine, phosgene (a choking agent) and mustard gas (which inflicts painful burns on the skin) were among the chemicals used. The results were indiscriminate and often devastating. Nearly 100,000 deaths resulted. Since World War I, chemical weapons have caused more than one million casualties globally.

As a result of public outrage, the Geneva Protocol, which prohibited the use of chemical weapons in warfare, was signed in 1925. While a welcome step, the Protocol had a number of significant shortcomings, including the fact that it did not prohibit the development, production or stockpiling of chemical weapons. Also problematic was the fact that many States that ratified the Protocol reserved the right to use prohibited weapons against States that were not party to the Protocol or as retaliation in kind if chemical weapons were used against them. Poison gasses were used during World War II in Nazi concentration camps and in Asia, although chemical weapons were not used on European battlefields.

The Cold War period saw significant development, manufacture and stockpiling of chemical weapons. By the 1970s and 80s, an estimated 25 States were developing chemical weapons capabilities. But since the end of World War II, chemical weapons have reportedly been used in only a few cases, notably by Iraq in the 1980s against the Islamic Republic of Iran.

Convention on the Prohibition of the Development, Production, Stockpiling and Use of Chemical Weapons and on Their Destruction

After 12 years of negotiations, the Chemical Weapons Convention (CWC) was adopted by the Conference on Disarmament in Geneva on 3 September 1992. The CWC allows for the stringent verification of compliance by State Parties. The CWC opened for signature in Paris on 13 January 1993 and entered into force on 29 April 1997. The CWC is the first disarmament agreement negotiated within a multilateral framework that provides for the elimination of an entire category of weapons of mass destruction by prohibiting the development, production, acquisition, stockpiling, retention, transfer or use of chemical weapons by States Parties.

According to article II of the Convention, chemical weapons means: a) Toxic chemicals and their precursors, except where intended for purposes not prohibited under this Convention, as long as the types and quantities are consistent with such purposes; b) Munitions and devices, specifically designed to cause death or other harm through the toxic properties of those toxic chemicals specified in subparagraph (a), which would be released as a result of the employment of such munitions and devices; c) Any equipment specifically designed for use directly in connection with the employment of munitions and devices specified in subparagraph (b).

In order to prepare for the entry-into-force of the CWC, a Preparatory Commission of the Organisation for the Prohibition of Chemical Weapons (OPCW) was established with the responsibility to prepare detailed operation procedures and to put into place the necessary infrastructure for the permanent implementing agency provided for in the Convention. Headquarters for this organization were established in The Hague, the Netherlands. The CWC entered into force on 29 April 1997, 180 days after deposit of the 65th instrument of ratification.

Organisation for the Prohibition of Chemical Weapons (OPCW)

With the entry-into-force of the Chemical Weapons Convention (CWC) on 29 April 1997, the Organisation for the Prohibition of Chemical Weapons (OPCW) was formally established.

The OPCW Technical Secretariat is located in The Hague, the Netherlands. Currently, 193 nations, representing about 98% of the global population, have joined the CWC. The OPCW mission is to implement the provisions of the CWC and to ensure a credible, transparent regime to verify the destruction of chemical weapons; to prevent their re-emergence in any member State; to provide protection and assistance against chemical weapons; to encourage international cooperation in the peaceful uses of chemistry; and to achieve universal membership of the OPCW. On 7 July 2023, the OPCW confirmed that 100% of the chemical weapons stockpiles declared by States Parties to the CWC have been verifiably destroyed, fulfilling an important stage in the Organisation’s work.

The cooperation between the United Nations and the Organisation for the Prohibition of Chemical Weapons is regulated by the relationship agreement between both organisations adopted by the General Assembly in September 2001. The close cooperation between the UN and the OPCW and the mutually reinforcing nature of their work was exemplified by the United Nations Investigation into the Allegation of the Use of Chemical Weapons in the Syrian Arab Republic (“Sellström Investigation”), the OPCW-UN Joint Mission and the work of the OPCW-UN Joint Investigative Mechanism (JIM).

Final Documents of the CWC Review Conference

View the final documents of the CWC review conference for 2023, 2018, 2013, 2008 and 2003.

Sellström Investigation

The United Nations Mission to Investigate Allegations of the Use of Chemical Weapons in the Syrian Arab Republic (“Sellström Investigation”) was established by the United Nations Secretary-General on 21 March 2013, following requests by the Syrian Arab Republic and other UN Member States to investigate separate allegations of the use of chemical weapons in the Syrian Arab Republic. The purpose of this specialized and impartial fact-finding mission, led by Professor Åke Sellström (Sweden), was to establish evidence related to the allegations of chemical weapons use. Upon the request of the Secretary-General, the Organisation for the Prohibition of Chemical Weapons (OPCW) and the World Health Organization (WHO) put their resources at the disposal of the UN Mission to support its investigation activities.

The UN Mission began its fact-finding activities in the Syrian Arab Republic on 19 August 2013. On the basis of the sufficiency and credibility of the information received, the UN Mission decided to investigate seven allegations reported to the Secretary-General. The Mission concluded that chemical weapons had been used in the conflict between the parties in the Syrian Arab Republic, in the Ghouta area of Damascus on 21 August 2013 and also on a smaller scale in Jobar on 24 August 2013, Saraqeb on 29 April 2013, Ashrafiah Sahnaya on 25 August 2013 and Khan Al Asal on 19 March 2013. The UN Mission’s final report (A/68/663-S/2013/735) was submitted on 12 December 2013.

The OPCW-UN Joint Mission for the Elimination of the Chemical Weapons Programme of the Syrian Arab Republic

The OPCW-UN Joint Mission for the Elimination of the Chemical Weapons Programme of the Syrian Arab Republic was formally established on 16 October 2013, a month after the Syrian Arab Republic deposited its instrument of accession to the Chemical Weapons Convention.

The mandate of the Joint Mission for an accelerated programme to completely eliminate the Syrian Arab Republic’s chemical weapons programme by mid-2014, derived from OPCW Executive Council decision EC-M-33/DEC.1 and UN Security Council resolution 2118 (2013). The Joint Mission was headed by the Special Coordinator, Ms. Sigrid Kaag (Netherlands). The OPCW-UN Joint Mission closed on 30 September 2014, although the OPCW continues to undertake the necessary residual activities required to fully implement Security Council resolution 2118 (2013). The OPCW confirmed the complete destruction of all chemical weapons declared by the Syrian Arab Republic on 4 of January 2016.

Pursuant paragraph 12 of resolution 2118 (2013) the Director-General of the OPCW has the obligation to report to the Security Council, through the UN Secretary-General, on the activities related to the implementation of this resolution. Accordingly, the High Representative for Disarmament Affairs briefs the Security Council Members, on a monthly basis, on the elimination of the Syrian Arab Republic chemical weapons programme.

The OPCW-UN Joint Investigative Mechanism

The Security Council adopted resolution 2235 (2015) on 7 August 2015, condemning “any use of any toxic chemical, such as chlorine, as a weapon in the Syrian Arab Republic”, and expressing determination to identify and hold accountable those responsible for such acts. In this resolution, the Security Council established the OPCW– United Nations Joint Investigative Mechanism (JIM) to “identify to the greatest extent feasible” those responsible. On 17 November 2016, the Security Council renewed the JIM’s mandate for a further period of one year by adopting resolution 2319 (2016).

The JIM succeeded in implementing its mandate to conduct impartial, objective investigations and was able to identify those responsible for six cases of chemical weapons use in the Syrian Arab Republic. Despite several proposals, the Security Council could not agree upon an extension of the JIM’s mandate. Consequently, the JIM ceased functioning on 17 November 2017.

The non-renewal of the mandate of the JIM left a gap in the ability of international organizations to identify those responsible for the use of chemical weapons. Therefore, in June 2018, the fourth Special Session of the Conference of States Parties to the Chemical Weapons Convention granted the Secretariat of the OPCW the authority to conduct such investigations. Pursuant to paragraph 10 of decision C-SS-4/DEC.3 the OPCW Secretariat established an Investigation and Identification Team (IIT) with the mandate to “identify the perpetrators of the use of chemical weapons in the Syrian Arab Republic by identifying and reporting on all information potentially relevant to the origin of those chemical weapons in those instances in which the OPCW Fact-Finding Mission in Syria determines or has determined that use or likely use occurred, and cases for which the OPCW UN Joint Investigative Mechanism has not issued a report”. On 8 April 2020, 12 April 2021, and 27 January 2023 the IIT released its reports.