The term Ultrasonic machining (USM) can be applied to any machining process which uses ultrasonic energy to erode brittle materials. The process has been successfully used to assist deburring, polishing, lapping, grinding, and drilling operations. Hardened steel, glass, ruby, and ceramics have been finish machined with a control of geometry and surface roughness under one micron. Applications have included optical products, dies and molds, structural ceramics and IC chips. The main topics of this article include machine tool renovation, work material application, accuracy of workpiece tolerance, the changing market and past research. Original developments in the Soviet Union, Germany, England, Japan, and the USA are surveyed. Possible areas of future research are identified.