Gamma-ray bursts (GRBs) have puzzled astronomers since their accidental discovery in the late 1960s. The BATSE detector on the Compton-GRO satellite has detected one burst per day for the last six years, revolutionizing our understanding of these objects. GRBs are found to be at cosmological distances, confirming their extragalactic origin. They release an enormous amount of energy, making them the most luminous objects in the universe. The simplest and most widely accepted interpretation is that GRBs result from the conversion of the kinetic energy of ultra-relativistic particles or the electromagnetic energy of a Poynting flux to radiation in an optically thin region, known as the "fireball" model. The "inner engine" that accelerates the relativistic flow remains hidden, but recent studies suggest it is associated with the formation of a compact object, likely a black hole. The temporal structure of GRBs reflects the activity of this inner engine, and recent observations of X-ray, optical, and radio counterparts support the fireball model. The nature of the inner engine is still uncertain, but binary neutron star mergers are a promising candidate. GRBs have implications for other areas of astronomy, such as gravitational lensing and cosmological parameters.Gamma-ray bursts (GRBs) have puzzled astronomers since their accidental discovery in the late 1960s. The BATSE detector on the Compton-GRO satellite has detected one burst per day for the last six years, revolutionizing our understanding of these objects. GRBs are found to be at cosmological distances, confirming their extragalactic origin. They release an enormous amount of energy, making them the most luminous objects in the universe. The simplest and most widely accepted interpretation is that GRBs result from the conversion of the kinetic energy of ultra-relativistic particles or the electromagnetic energy of a Poynting flux to radiation in an optically thin region, known as the "fireball" model. The "inner engine" that accelerates the relativistic flow remains hidden, but recent studies suggest it is associated with the formation of a compact object, likely a black hole. The temporal structure of GRBs reflects the activity of this inner engine, and recent observations of X-ray, optical, and radio counterparts support the fireball model. The nature of the inner engine is still uncertain, but binary neutron star mergers are a promising candidate. GRBs have implications for other areas of astronomy, such as gravitational lensing and cosmological parameters.