Sputtering of solid surfaces by low-energy ion beams can remove materials at a rate useful for machining purposes; the system can be called an ion-milling machine. Milling of solid materials, with minimum change to adjacent materials, is possible by this method. The first part of the paper discusses the parameters involved in ion interactions with solid surfaces. Six different ion-milling techniques and ion sources are next described. Finally, practical procedures obtained with some current problems are given.