Optical interferometric techniques are more sensitive, accurate, precise and whole field in comparison to other conventional measurement techniques. These techniques are non-contact type and non-invasive. Digital holography has made possible the quantitative measurement of phase from a single hologram. This has provided a very powerful tool for optical metrology. Freedom from processing of recording material and direct availability of phase from one digital hologram has made interferometric processes faster, robust and almost real time. This book provides brief introduction of conventional holography and detailed description of digital holography including brief history of its development. Further, it provides a brief description of different digital recording process and numerical reconstruction techniques in optical metrology. Also two important industrial (measurement of diffusion coefficient and visualization of drying process, crack in the surface of the paint and disbonding of the paint on the surface) and two scientific (swept source digital holography and filtering technique) applications of digital holography have been provided.