One astrophysical source of uncertainty in supernova observations comes from cosmic dust particles. Dust in the circumstellar (CS) environment of SNe, in the insterstellar medium of SN host galaxies and possibly even in the intergalactic medium have important implications for the observed colors and luminosities of SNe Ia; typically making them redder and fainter.

By measuring the wavelength dependence of the dust extinction from UV-to-IR observations and using other proxies for dust (such as Sodium absorption lines in high-resolution spectra) there is increasing evidence that some SNe show evidence for unusual dust. This, together with time-varying blue-shifted Sodium absorption, could indicate the presence of dust in the CS environment. Detecting or constraining the amounts of CS dust also has implications on the progenitor systems.