Electrochemical mechanical polishing (ECMP) is a composite machining method, which combines electrochemical and mechanical polishing methods, and was proposed for conductive materials with high hardness, high brittleness, and high chemical inertness. This method uses electrochemical method to modify the workpiece surface and employs mechanical action to remove the modified layer, thus realizing polishing of the workpiece. ECMP combines the advantages of electrochemical machining and mechanical machining, and can obtain high-efficiency, high-precision, and low-cost polishing compared with traditional chemical mechanical polishing method. This chapter divides ECMP into loose- and fixed-abrasive ECMP according to the applied polishing medium and introduces their applications in the polishing of metals and semiconductors, their latest research progresses, and their advantages and disadvantages, at the same time also introduces their polishing mechanism of different materials. In addition, recently developed new technologies of ECMP are also reviewed. Lastly, the development trends and application prospects of ECMP are discussed.