Emerging possibilities of using ultrashort pulse lasers as a new light source for advanced optical metrology are addressed in comparison to traditional sources such as CW lasers and white light. Emphasis is on explaining various principles of absolute distance interferometry that become practical by exploiting the unique nature that a train of ultrashort pulses is a phase-locked combination of a large number of monochromatic laser lines evenly spaced over a wide spectral range. In that context, adopting a single ultrashort pulse laser offers many new opportunities of performing absolute distance measurements with sub-wavelength resolutions over extensive ranges. It is also discussed that the new light source allows one to improve the measuring performances of other fields of optical metrology such as large-scale surface profiling.