This chapter briefly discusses the application, chemical properties and physical properties of phosgene. It presents detailed information on the air analysis of phosgene. Phosgene is formed in air in trace amounts by photodecomposition of chlorinated solvent vapors, used in the synthesis of dyes and pesticides, and as a war gas. It is slightly soluble in water, soluble in hexane, benzene, and glacial acetic acid. Phosgene is colorless with suffocating odor and sweet hay-like odor at low ppb concentration and highly poisonous. During the air analysis of phosgene, air is drawn through a midget impinger containing 10 mL of 2" aniline in toluene. Phosgene reacts with aniline to form carbanilide. Carbanilide is analyzed by reverse-phase high-performance liquid chromatography (HPLC) with an UV detector. Alternatively, air is also drawn through a midget impinger containing a 10" solution of equal parts of ρ-dimethylaminobenzaldehyde and diphenylamine in carbon tetrachloride.