This review is devoted to the chemistry of hydrogen bis(fluorosulfonyl)imide (HFSI) and its derivatives. HFSI is a valuable fluorine containing compound and in recent years, the interests in HFSI have been concentrated on the preparation of its metallic salts, ionic liquids, eutectic mixtures, which are used in electronics. HFSI is a colorless liquid, m.p. 17 degrees C, b.p. 170 degrees C, density 1.89 g/cm(3). HFSI is a strong acid with pK(a) = 1.28 (water). It is very soluble in water and in various organic solvents such as dichloromethane, chloroform, dimethylcarbonate, acetonitrile, ethyl acetate. Hydrolysis in water is relatively very slow at low temperature. Herein, advances in chemistry of hydrogen bis(fluorosulfonyl)imide and its derivatives, the literatures details of past two decades have been summarized with the aim of having useful literature information to the scientific community.