The advent of diamond turning is one of the most significant breakthroughs in modern materials processing technology, especially for ultraprecision applications that demand extreme form accuracy and surface finishing. This chapter emphasizes the operating principles of diamond turning in which the underlying mechanics of material removal are governed by the tool edge radius and microstructural effects. Recent advances in diamond turning, particularly in productivity improvement for some important applications through high-volume production, are addressed. The design principles of both the machine tool and cutting tool, which are critical components of a diamond turning system, are also explained in sufficient depth. Despite that, the latest advancements in slow tool servo technology, a widely applied method for manufacturing large nonrotationally symmetric parts, are also comprehensively detailed. Finally, considering the increasing demand for complex optics, there is also a brief introduction to the recent advances of the fast tool servo turning technology.