Single-point diamond machining is a versatile technique for producing metal optics in conventional as well as unusual shapes. The diamond-turning process is now well enough understood and controlled that specular, low-scatter surfaces can be produced. However, the grooved nature of the surfaces makes it difficult to relate some of the surface characterization parameters used for polished optics to the performance of the diamond-turned parts in an optical system. For example, surface roughness derived from total integrated scattering measurements may be much different from the measured profile roughness. Thus it is important to understand the physical mechanisms involved in the various surface character-ization parameters such as total and angular scattering, reflectance, and absorption and their relation to the microtopography and metallurgical structure of the diamond-turned surfaces. The significance of the surface characterization will be discussed and examples of characterization techniques useful for diamond-turned optics will be described.