Compounds containing carbon-nitrogen bonds, such as amines, imines, nitriles, and N-heterocycles, are widespread in nature and play essential roles in pharmaceuticals, pesticides, materials, and other fields. The investigation of reactions involving carbon-nitrogen bonds is of paramount significance. In organic synthesis, the reduction of carbon-nitrogen bonds can be used for the removal of protecting groups, conversion of functional groups, and construction of biologically active molecules. However, carbon-nitrogen bonds, especially carbon-nitrogen single bonds, are renowned for their notable stability, thus requiring the harsh conditions for their reductions. As the renaissance of organic electrosynthesis in recent years, the electrochemical cathodic reductive reactions of carbon-nitrogen bonds under mild conditions have garnered considerable attention. According to the molecular structure of the substrates, electrochemical cathodic reductive reaction involving carbon-nitrogen bonds can be classified into two major categories: reductions of saturated carbon-nitrogen bonds, and unsaturated carbon-nitro- gen bonds. For compounds with saturated carbon-nitrogen bonds, such as ammonium salts, amides, aziridines, and nitro compounds, their cathodic reductions usually involve the cleavage of carbon-nitrogen bonds and substitution of the N-contained functional group. Compounds with unsaturated carbon-nitrogen bonds, such as imines, oximes, and N-heterocycles, are typically reduced into intermediates containing carbon-nitrogen single bonds, followed by addition reactions. A concise overview of the cathodic reductive reactions of above two kinds of substrates is provided and the possible reaction mechanisms is summarized.

Key words: organic electrochemistry, cathodic reduction, carbon-nitrogen bond, radical ions