The use of special machine tools with single-crystal diamond-cutting tools to produce metal optics is called diamond turning. The manufacture of optical surfaces by diamond turning is relatively new compared to the traditional optical-polishing methods. In terms of geometry and motions required, the diamond-turning process is much like the step of generating the optical surface in traditional optical fabrication. However, the diamond-turning machine is a more sophisticated piece of equipment that produces the final surface, which typically does not need the traditional polishing operation. But surface quality produced by the best diamond turning does not yet match the best conventional-polishing practice. Yet. the limits of diamond turning for both figure and surface finish accuracy have not yet been reached. There are several important advantages of using diamond turning, including the ability to produce good optical surfaces to the edge of the clement, to fabricate soft ductile materials difficult to polish, to eliminate alignment in some systems, and to fabricate shapes difficult to do by other methods. If the advantages of diamond turning suggest this fabrication method, then it is important to determine early in the design phase of a project whether the material specified is appropriate for diamond turning.