A technique for recording, and later reconstructing, the amplitude and phase distributions of a coherent wave disturbance. Invented by Dennis Gabor in 1948, the process was originally envisioned as a possible method for improving the resolution of electron microscopes. While this original application has not proved feasible, the technique is widely used as a method for optical image formation, and in addition has been successfully used with acoustical and radio waves. This article discusses holography with electromagnetic waves in the optical and microwave regions of the electromagnetic spectrum, and its potential use with x-rays. For holography with sound waves.