August 21, 2013, Ghouta, Syria.

The Ghouta chemical attack took place on 21 August 2013 during the Syrian Civil War, when several areas of Ghouta, a group of suburbs east and southwest of Damascus, were struck by chemical weapons. United Nations investigators later concluded that surface-to-surface rockets containing the nerve agent sarin had been used in Ein Tarma, Moadamiyah and Zamalka. The attack caused mass casualties, overwhelmingly among civilians, and medical personnel reported symptoms consistent with exposure to a nerve agent. The UN's investigation found sarin in biomedical and environmental samples, as well as in examined rocket fragments.

The precise death toll remains disputed because the affected areas had limited medical facilities and the investigation could not establish the full extent of the casualties. Contemporary investigations nevertheless documented hundreds of deaths and thousands of people suffering symptoms consistent with chemical exposure.

The lowest death tolls, reported by France and the United Kingdom, put the number of civilians killed at between 281 and 350, while the highest figures, reported by the United States and the now-defunct Free Syrian Army (FSA), recorded 1,429 and 1,729 victims, respectively.
In addition, approximately 3,600 patients were documented with neurotoxic symptoms at three hospitals supported by the French organization Doctors Without Borders (MSF).

The attack became one of the most significant incidents of the Syrian Civil War and triggered a major international crisis over Syria's chemical-weapons programme. The UN confirmed that chemical weapons had been used but did not itself determine who was responsible; subsequent investigations and governments reached different conclusions about attribution. The UN Secretary-General described the use of chemical weapons as a war crime and a grave violation of international law.