  Supernova flux and polarization spectra bring vital information on the
geometry, physical conditions, and composition structure of the ejected matter.
For some supernovae the circumstellar matter is also probed by the observed
spectra. Some of this information can be inferred directly from the observed
line profiles and fluxes, but because of the Doppler broadening and severe line
blending, interpretation often involves the use of synthetic spectra. The
emphasis in this Chapter is on recent results obtained with the help of
synthetic spectra.
