A fundamental, profound review of the key issues relating to the early universe and the physical processes that occurred in it. The interplay between cosmic microwave background radiation, large scale structure, and the dark matter problem are stressed, with a central focus on the crucial issue of the phase transitions in the early universe and their observable consequences: baryon symmetry, baryogenesis and cosmological fluctuations. There is an interplay between cosmology, statistical physics and particle physics in studying these problems, both at the theoretical and the experimental / observational levels. Special contributions are devoted to primordial and astrophysical black holes and to high energy cosmic rays and neutrino astrophysics. There is also a special section devoted to the International Space Station and its scientific utilization.