  The effects of dust opacity on the radiation of nearby and distant galaxies
are reviewed. The geometrical distribution of the dust inside the galaxy plays
a fundamental role in determining the wavelength dependence of the obscuration
and the opacity of the galaxy. In the local Universe, late Hubble type galaxies
appear to contain enough dust that corrections for the effect of obscuration
become important. This is true expecially at blue and UV wavelengths, i.e. in
the wavelength range of interest for studies of massive stars and star
formation processes. Multiwavelength observations provide a powerful tool for
characterizing the reddening caused by dust. A `recipe' is given for removing
the dust reddening and recovering the UV and optical light in star-forming
galaxies.
