Based on IRAS data, the mid-infrared spectral range was thought to be the domain of small fluctuating grains and Aromatic Features in Emission (AFE) as far as the interstellar medium (ISM) was concerned (Beichman 1987; Puget & Léger 1989). Since the integrated emission from normal galaxies is dominated by the ISM in this range, ISO has been able to address quantitatively the energy budget of the ISM across various emission components, to investigate the variation of this budget among galaxies, and to contrast these properties with those of galaxies illuminated by Active Nuclei. This section will expand on the first two of these three areas.