The basic concepts of optical holography stem from the 1949 work of Gabor and the 1962 work of Leith and Upatnieks. In 1965, Homan suggested the application of holography to Mach-Zehnder interferometry and Powell and Stetson invented holographic interferometry as we know it today. This gave us the ability to optically determine deformation and displacement of diffusely reflecting opaque objects. The basic principles of quantitative interpretation of fringes produced by holographic interferornetry are now well known and can be expressed in a number of formulations. A variety of refinements and extensions have been developed during the past two decades including optical derotation, the introduction of fiber optics, the application to computer tomography, the development of heterodyne holographic interferometry and the introduction of various recording media.