Solution chemistry of Se(IV), in particular the acid-base properties, salt and complex formation, chemical reduction and reaction of Se(IV) with organic and inorganic sulfur compounds are briefly summarized. The electrochemical reduction of Se(IV) on dropping and stationary mercury electrodes is dealt with in some detail. The effects of antecedent acid-base equilibria and of consecutive reactions of the reduction product, Se(2-), adsorption of their products, and effects of added metal ions are discussed. The principles and applications of stripping analyses for determination of ultratraces of Se(IV) are summarized. The behavior on unreactive (Au, Pt, carbon) and reactive (Hg, Ag, Cu) electrodes are compared.