  The relationship between star formation and infrared emission in galaxies
will be investigated. If galaxies were simple objects and young stars were
completely covered with dust, then all the absorbed light of the young stars
would be re-emitted in the infrared and from the infrared emission of galaxies
we would infer the star formation rate (SFR) in them accurately. To show the
complexities involved in real galaxies, we will use as a case study the
late-type spiral galaxies. We will show that the heating of the dust is done
mainly by the UV radiation of the young stars and therefore the infrared
emission reveals the SFR in them. With a realistic model and its application to
a number of galaxies, tight correlations are derived between SFR and total far
infrared luminosity on one hand, and dust mass and 850 micron flux on the
other. Other diagnostics of the SFR are examined and it is shown that there is
consistency among them. Thus, the SFR for galaxies of all Hubble types has been
determined as well as for interacting starburst galaxies. Combining different
methods, the star-formation history of the universe has been determined and
will be shown. Finally, some early results from the Spitzer Space Telescope
will be presented.
