The sources of the Cosmic Infrared Background
  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 reviewed in this paper. Among others, we emphasize a new Spitzer result based on a Far-IR stacking analysis of mid-IR sources. 
G. Lagache (1), H. Dole (1), J.-L. Puget (1) ((1) Institut   d'Astrophysique Spatiale, Orsay, France)