A decades-long policy of ambiguity means that Israel's chemical arsenal remains the subject of speculation.
An audio version of an in depth article on the story of how the nerve agent used in an attack on former Russian spy Sergei Skripal was developed.
A legal expert explains why Russia's accusations that the UK breached international law are unfounded.
International law on chemical weapons fails without mutual trust and transparency.
The recent American airstrike in Syria has created a new norm in international law sanctioning the unilateral use of force to punish those who deploy chemical weapons against their own people.
Using nerve agents is banned under the Chemical Weapons Convention, but North Korea is not a party to it.