The field of diffractive optics is at the same time old and young. Diffraction gratings have been known for two centuries and used extensively in spectroscopy, for example. Also the theoretical understanding of the basic properties of grating diffraction has been well developed since that time. Until the 1960s, the technological foundation of grating manufacture used to be precision mechanics. It was then, when with the advent of the laser, things gradually started to change. On the one hand, laser interferometry became an additional tool to fabricate grating structures with very small periods. On the other hand, many new applications for optics started to develop based on the use of different types of laser sources. Some examples that may be mentioned are—besides modern spectroscopic techniques—areas like material processing, optical communications and information processing, optical data storage, etc. Consequently, the term “diffractive optics” has obtained a different flavor during the past 20–30 years. New types of diffractive elements were being developed with new technologies. This started in the mid-1960s with the invention of computer-generated holography which allowed to create “arbitrary” wavefronts (this means, within practical limits) by diffracting a light wave at an irregular binary structure. The computation and fabrication of computer-generated holograms was made possible by then newly available digital computers and plotting equipment. Since the early 1970s, people started to make diffractive elements using microfabrication techniques (lithography, etching, etc.) adapted from the processing of electronic circuits. These ideas were initially demonstrated in industrial research laboratories like Philips and Thomson-CSF.