Abstract :
Mid- and far-infrared spectroscopy of galaxies has become possible for sizeable samples with the advent of the Infrared Space Observatory ISO. This paper discusses diagnostics based on emission lines and the mid-infrared emission and absorption features, and their application to starburst galaxies, AGN, and ultra-luminous infrared galaxies. The improved understanding of infrared galaxies that has been gained on the basis of the ISO data is of particular relevance for the understanding of the recently discovered infrared galaxies at high redshift.
