  We review the evolution of the interstellar medium in disc galaxies, and
show, both analytically and by numerical 3D hydrodynamic simulations, that the
disc-halo connection is an essential ingredient in understanding the evolution
of star forming galaxies. Depending on the star formation rate of the
underlying gaseous disc, a galactic fountain is established. If the star
formation rate is sufficiently high and/or cosmic rays are well coupled to the
thermal plasma, a galactic wind will be formed and lead to a secular mass loss
of the galaxy. Such a wind leaves a unique imprint on the soft X-ray spectra in
edge-on galaxies, with delayed recombination being one of its distinctive
features. We argue that synthetic spectra, obtained from self-consistent
dynamical and thermal modelling of a galactic outflow, should be treated on an
equal footing as observed spectra. We show that it is thus possible to
successfully fit the spectrum of the starburst galaxy NGC 3079.
