This article addresses the state-of-the-art in optical mask CD metrology based on the most recent deep ultraviolet (DUV) microscope optics operating at 248 nm. It further points out the future potential and limitations of optical CD metrology in general and shows that DUV mask metrology has all of the capabilities to meet the ITRS needs, while avoiding the difficulties associated with scanning electron microscopy based metrology tools, including substrate charging and contamination.