We have developed four methods of solid oxide electrochemical doping (SOED) using solid oxide electrolytes such as M-β“-Al₂O₃ and Y(Ca)-stabilized ZrO₂. The basic mechanisms of the SOED methods were explained and some results were demonstrated. SOED 1 and 2 are very useful doping methods, because various ceramics can be doped with various cations. SOED 1 is based on the electro-substitution mechanism, where the Mⁿ⁺ cation can be doped into ceramics together with the substitution of a cation in the ceramics. SOED 2 is based on the electro-bi-injection mechanism, where the Mⁿ⁺ cation can be injected into the ceramics together with the injection of an oxygen anion. Some important advantages were demonstrated compared with the conventional doping method. The SOED method will bring about a revolution in ceramic synthesis in the near future.