In this paper, a comprehensive introduction of micro milling technology, which is a novel micro-manufacturing technology to fabricate many materials with complex 3D and high aspect ratio structure, is presented. Compared with some other micro-manufacturing technologies, micro milling has a lot of merits, such as low cost, flexibility. The machine tool, micro mills, and monitoring devices are the key technologies, and the micro milling principles with attention to minimum chip thickness and workpiece microstructure influences are presented primarily. At last, our research in micro milling field is given.