This volume covers a number of areas of high-energy astrophysics, focusing on the status of the field, outstanding problems to be resolved and experiments that should be providing some answers in the 21st century. The following topics are featured: high-energy frontier, including the enigmatic observations of events beyond the cut-off energy; gamma-ray bursts - local and cosmological models; high-energy astrophysical neutrinos; cosmic ray matter and antimatter; solar system astrophysics; and galactic physics.