673 AD
First use of "Greek Fire" at the siege of Constantinople.

...

1899
An international peace conference held in The Hague leads to an agreement prohibiting the use of projectiles filled with poison gas.

April 1915
Chlorine gas attack at the battle of Ypres, Belgium (World War I).

July 1917
First use of mustard gas at the second battle of Ypres.

1918
By the end of World War I, the use of over 100,000 tonnes of toxic chemicals during the war had resulted in the deaths of 90,000 soldiers, and had caused more than a million casualties.

1925
The Geneva Protocol is concluded. This treaty bans the use of both bacteriological and chemical weapons but is not enough to stop countries from producing, using and stockpiling chemical weapons thereafter.

1972
The countries of the world conclude the Biological and Toxin Weapons Convention in Geneva and commit themselves to continue negotiations on a treaty to ban chemical weapons as well.

1988
Iraq uses chemical weapons against its own Kurdish citizens in the town of Halabja.

1992
The negotiators in Geneva agree on the text of the Convention on the Prohibition of Development, Production, Stockpiling, and Use of Chemical Weapons and on Their Destruction (Chemical Weapons Convention).

1993
The Chemical Weapons Convention is opened for signature at a January signing ceremony in Paris; 130 countries show support for the CWC and for international disarmament by signing the Convention. In February 1993, a Preparatory Commission is set up in The Hague to prepare for the entry into force of the Convention.

1995
In Japan, the Aum Shinrikyo cult releases the chemical agent sarin in a terrorist attack on the Tokyo subway. About five thousand people become sick and a dozen are killed.

1997
The Chemical Weapons Convention enters into force for 87 member countries. The Organisation created by the Convention to carry out the terms of the Convention, the Organisation for the Prohibition of Chemical Weapons (OPCW), opens its headquarters in The Hague.