Very high-energy gamma-ray astronomy

Very high-energy gamma-ray astronomy has emerged as an exciting and vital field. In the last seven years, major discoveries have been made by experiments in space and on the ground. In space, instruments on the Compton Gamma Ray Observatory have identified high-energy emission from a variety of astrophysical sources, including gamma-ray bursts, spin-down pulsars, and active galaxies of the blazar type. Remarkably, a number of these sources have now been detected at much higher energies by ground-based instruments. This review will concentrate on the methodology and results from these ground-based experiments, currently operating at energies above 250GeV. The ground-based detections are for the first time statistically compelling and stand in direct contrast to earlier results reported in the 1980s. The future scientific and experimental prospects for the field appear excellent and are summarized.