ISOPHOT has not only advanced the knowledge of IR properties of normal galaxies but has also made unexpected discoveries. The bulk of the emission from dust has been measured, revealing cold dust in copious quantities. This dust is present in all types of normal galaxies and is predominantly distributed in a diffuse disk with an intrinsic scalelength exceeding that of the stars. Cold dust has been found beyond the optical regions of isolated galaxies, associated with the extended HI disks of spiral galaxies or with the HI envelopes of dwarf galaxies. The fraction of the bolometric luminosity radiated by dust has been measured for the first time. Realistic geometries for stars and dust have been derived from ISOPHOT imaging observations, enabling the contribution of the various stellar populations to the dust heating to be accurately derived. This enormous advancement in the understanding of normal galaxies in the nearby Universe has laid the foundation for more detailed investigations with Spitzer and Herschel. A clear priority is to increase the number of galaxies with detailed imaging information and to provide better statistics on carefully selected samples, especially those selected in the optical/NIR bands. Ultimately, the improved sensitivity of the new infrared space observatories will allow knowledge of the dust emission from normal galaxies to be extended beyond the nearby universe.
Acknowledgments The authors would like to take this opportunity to thank all the individuals that helped make the ISO mission a success. R.J. Tuffs and C.C. Popescu would also like to thank Heinrich J. Völk for enlightening discussions.