Hydrazines are versatile building blocks in organic synthesis. They are not only widely used for the preparation of numerous nitrogen-containing compounds, but also as coupling partners via denitrogenation in transition metal-catalysed coupling reactions. Recently, they have gained considerable attention as radical precursors for the formation of carbon–carbon and carbon–heteroatom bonds with or without release of nitrogen gas under the photochemical and electrochemical conditions. In this review, we will focus on the recent radical coupling reactions via photochemical and electrochemical strategies, and as well as discussion of their mechanisms.