Recent advances in thin film fabrication techniques have made multilayer mirrors an important new addition in the field of soft x-ray diffraction optics. A multilayer is a one-dimensional periodic structure that consists of an alternating sequence of high and low atomic number elements evaporated or sputtered onto a substrate. Characterization of these devices has been carried out on a variety of x-ray sources, including synchrotron radiation, over a large range of parameters. Extensive modeling of the diffraction characteristics of multilayers has shown that the theory of optics of thin films gives good agreement between measured and calculated diffraction profiles. Application of multilayer mirrors as normal incidence x-ray collectors, monochromators, and beam splitters is being explored.