Fundamental descriptive rugate filter parameters and concepts are shown. A simple rugate filter is derived from the Fourier analysis of a high/low refractive index pair used in a conventional non quarter-wave stack design. Progress in both design and fabrication is demonstrated by representative rugate filters which function in either the visible or infrared. Numerous examples are cited to show the utility of refractive index profile tailoring and the advantages of using this technology.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.