Gamma–ray bursts, an enigma for more than 25 years, are now coming into focus. They involve extraordinary power outputs, and highly relativistic dynamics. The ‘trigger’ involves stellar–mass compact objects. The most plausible progenitors, ranging from NS–NS mergers to collapsars (sometimes called ‘hypernovae’) eventually lead to the formation of a black hole with a debris torus around it, the extractable energy being up to 1054 erg. Magnetic fields may exceed 1015 G. Details of the afterglow may be easier to understand than the initial trigger. Bursts at very high redshift can be astronomically important as probes of the distant Universe.