The book discusses the preliminary results of the COBE satellite (Cosmic Background Explorer). First, the three instruments on board COBE: FIRAS (Far Infrared Absolute Spectrophotometer), DMR (Differential Microwave Radiometer), DIRBE (Diffuse Infrared Background Experiment), and the data acquisition and reduction techniques, are described by members of the COBE Science Team. Most of the subsequent material is devoted to the cosmological implications of the observations. The topics covered are: the Early universe: Planck era, inflation, dark matter, relic particles, etc. large and small scale anisotropies of the CMB large-scale structures and galaxy formation infrared to submillimetre background dust in galaxies and quasars instrumentation and observation techniques Scientists of different communities, from particle physics to observational astrophysics, have been enabled to share their convictions and their doubts about the `excess of perfection' of the relic Cosmic Radiation. Only such opportunities will allow us to make progress in the understanding of our Universe.