  The discovery of the Cosmic Infrared Background (CIB) in 1996, together with
recent cosmological surveys from the mid-infrared to the millimeter have
revolutionized our view of star formation at high redshifts. It has become
clear, in the last decade, that a population of galaxies that radiate most of
their power in the far-infrared (the so-called ``infrared galaxies'')
contributes an important part of the whole galaxy build-up in the Universe.
Since 1996, detailed (and often painful) investigations of the high-redshift
infrared galaxies have resulted in the spectacular progress covered in this
review. We outline the nature of the sources of the CIB including their
star-formation rate, stellar and total mass, morphology, metallicity and
clustering properties. We discuss their contribution to the stellar content of
the Universe and their origin in the framework of the hierarchical growth of
structures. We finally discuss open questions for a scenario of their evolution
up to the present-day galaxies.
