Intensity-fluctuation spectroscopy (IPS) is usually considered to be complementary to conventional spectroscopy and capable of removing technical restrictions on the resolving power. However, the information provided by field spectroscopy is identical to that obtained by IFS only for fields with Gaussian statistics. For non-Gaussian fields, IFS yields essentially new information, and the present review is devoted to this aspect of IFS. It surveys experiments concerned with the investigation of the noise spectrum of resonance fluorescence and of coherent forward scattering by an atomic vapor, which provide data on the width and the structure of levels involved in atomic transitions under the conditions of dominant Doppler broadening. Fundamental and technical limitations of the method are examined. Analogous studies of fluctuation spectra of radiation scattered by macroparticles in liquids can be used to determine the time dependence of the particle form factor independently of the characteristics of translational diffusion.