The existence of materials with very high specific energies greatly exceeding the local virial temperature is best represented by cosmic rays, whose origin has long been a mystery. Recent astrophysical observations in X-ray, gamma-ray, neutrino, and high energy cosmic ray experiments, in conjunction with theoretical studies, have revealed various new aspects of the high energy universe, including promising candidates for cosmic ray acceleration sites. As each approach has its own advantages and limitations, it is expected that joint efforts by experimentalists and theorists in various related...