  Following on from IRAS, ISO has provided a huge advancement in our knowledge
of the phenomenology of the infrared (IR) emission of normal galaxies and the
underlying physical processes. Highlights include: the discovery of an extended
cold dust emission component, present in all types of gas-rich galaxies and
carrying the bulk of the dust luminosity; the definitive characterisation of
the spectral energy distribution in the IR, revealing the channels through
which stars power the IR light; the derivation of realistic geometries for
stars and dust from ISO imaging; the discovery of cold dust associated with HI
extending beyond the optical body of galaxies; the remarkable similarity of the
near-IR (NIR)/ mid-IR (MIR) SEDs for spiral galaxies, revealing the importance
of the photo-dissociation regions in the energy budget for that wavelength
range; the importance of the emission from the central regions in shaping up
the intensity and the colour of the global MIR luminosity; the discovery of the
``hot'' NIR continuum emission component of interstellar dust; the predominance
of the diffuse cold neutral medium as the origin for the main interstellar
cooling line, [CII] 158 micron, in normal galaxies.
