Three generations of empirical scaling equations, developed by the Strong Motion Research Group at University of Southern California in the 1970’s, 1980’s and 1990’s, for the attenuation and scaling of spectral amplitudes of strong ground motion are reviewed. Semi-theoretical extrapolation functions for extending these empirical scaling equations to high and low frequencies are also presented. For brevity, only equations and illustrations which describe the relative response spectrum amplitudes are shown, but the methods and procedures presented are also applicable to scaling of Fourier amplitude spectra, for which complete corresponding references are also included.