Wavelength filters permit the separation of anomalies of different horizontal extents on magnetic and gravity maps. They can be used equally well for structural and topographic maps or for any other type of data amenable to gridding.Practical filters were developed following two series of cutoff wavelengths. Of special interest is the small size of the filters as compared to the steepness and smoothness of their wavenumber characteristics. Filters for any desired wavelengths can easily be derived from the described coefficient sets.Examples are given for the application of filters which can be used as regional, residual, and band-pass filters. The resultant maps are in the same units as the original maps. A given map can be divided into several wavelength components, and the sum of the components is equal to the original data. The method is shown to be versatile, and second-derivative calculations can be approximated by a properly chosen residual filter.