Published online by Cambridge University Press: 14 August 2015
Based on results from the first half of its mission, ISO (Kessler et al. 1996) is contributing to our understanding of normal galaxies by offering effective gauges of the physical conditions within the interstellar medium (ISM) of galaxies. ISO data permit a more precise and detailed characterization of the radiation, dust and gas deep within many more galaxies than had been previously possible. This in turn yields new insight into the regulation mechanisms of star formation and galaxy evolution. Apart from these ISM diagnostics, ISO also contributes a vastly improved empirical description of galaxies at all infrared wavelengths, which will be critical in guiding the search for the origins and early life of galaxies.