Multilayer structures are now of sufficient quality to be applied as optic elements in high performance instrumentation. Additionally, the range of materials used in multilayer construction has significantly broadened so that optimum performance is achievable in the soft x-ray and extreme ultraviolet. Calculated ideal reflection efficiencies for the spectral range 100 to 2000 eV and examples of the predicted performance of several specific material pairs are presented first. A short summary of multilayer synthesis procedures is then given. A simple schematic model of a multilayer structure is described and used as a basis for discussing the variety of imperfections that limit multilayer performance. Application of multilayer diffraction gratings to the determination of soft x-ray and ultraviolet optical constants is then discussed. Recent advances in multilayer synthesis technology are then described. The paper is summarized with a consideration of advanced multilayer optics, optical systems and new directions.