Analytical expressions in the time and frequency domains are derived for non-Debye relaxation processes. The complex frequency dependent susceptibility function for the stretched exponential relaxation function is given for general values of the stretching exponent in terms of -functions. The relaxation functions corresponding to the complex frequency dependent Cole-Cole, Cole-Davidson and Havriliak-Negami susceptibilities are given in the time domain in terms of -functions. It is found that a commonly used correspondence between the stretching exponent of Kohlrausch functions and the stretching parameters of Havriliak-Negami susceptibilities are not generally valid.