Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Chemical weapons are defined as toxic chemicals which can be used in warfare or crowd control. A chemical weapon can incapacitate, harm or kill the enemy. It is believed that the era of chemical warfare began during the World War I, with the German army’s chlorine attack at Ypres, Belgium, in spring, 1915. Thanks to the Geneva Protocol signed in 1925, the use of chemical and biological weapons is banned in war.