  We present the results obtained through the various ISO extragalactic deep
surveys. While IRAS revealed the existence of galaxies forming stars at a rate
of a few tens (LIRGs) or even hundreds (ULIRGs) solar masses in the local
universe, ISO not only discovered that these galaxies were already in place at
redshift one, but also that they are not the extreme objects that we once
believed them to be. Instead they appear to play a dominant role in shaping
present-day galaxies as reflected by their role in the cosmic history of star
formation and in producing the cosmic infrared background detected by the COBE
satellite in the far infrared to sub-millimeter range.
