Properties of radiation generated by fluctuating sources of different states of coherence will be investigated. The effects of spatial and temporal correlations of source fluctuations on spectra of emitted light will be studied. The aim is to provide a theoretical basis for spectroscopy of partially coherent sources. Further, the techniques of modern coherence theory will be used to develop a treatment of scattering of polychromatic light of any state of coherence from media which exhibit spatial and temporal statistical fluctuations in their macroscopic parameters. A concept of instantaneous cross-spectral density will be applied to propagation of very short optical pulses, specifically to a study of how the instantaneous spectrum of a light pulse changes in the process of propagation.