**Abstract**

Ultra precision diamond turning is one of the advanced techniques to generate highly finished optical grade surfaces. The machining at nano scale requires extremely small material to be removed which poses a severe challenge on the cutting tool. At nanoscale, the material strength becomes multi fold and it becomes extremely difficult to remove the material. A machining rule is that the tool must be harder than the workpiece. Diamond is the hardest known natural material. Thus at nano scale, single crystal diamond is commonly used as a cutting tool to remove the unwanted material from the work-piece. There are different orientations of the diamond cutting tool which are utilized depending on the work-piece being machined. Although diamond is the hardest, still there are various challenges in machining different kinds of materials from metals to semiconductors. Diamond machined work-piece surfaces find applications in a range of sectors from energy sector to biomedical and defense to optics industries. The present chapter covers the various aspects of single crystal diamond tool in ultra- precision machining. Tool-workpiece material interaction, material removal mechanisms and tool wear are some of the issues which have been covered in detail.

**Keywords:** diamond turning, tool wear, cutting mechanism, precision machining, nanoscale machining, single crystal diamond, diamond tool
