Chemical Warfare: an Introduction to Mustard Gas | Chemically Speaking: the Structure of Mustard Gas | By Any other Name: Origins of Mustard Gas | In Flander’s Field: Mustard Gas Affects History | Agent of War to Anti-Cancer Drug: History Affects Mustard Gas | Taking the Next Step: More Sources on Mustard Gas
Molecule of the Month – Mustard Gas: A great overview site.
The Medical Aspects of Gas Warfare: A collection of primary source documents about the impact of chemical warfare during World War I.
Facts about Sulfur Mustard: CDC fact sheet.