On 30 June 1908 a mysterious fireball exploded in the Siberian sky and flattened 2,000 square kilometres of the remote Tunguska forest. As no crater and no material from outer space were ever found, a meteorite could not have caused the Tunguska explosion. So what did? This 'grand dame of science mysteries' soon turns 100 but continues to seduce scientists and charlatans alike, all hoping to explain what caused the explosion. The scientists' suspects include a comet, an asteroid, a mini black hole, a rock of antimatter, a mirror matter asteroid, and a methane gas blast from below. X-files-type explanations include an alien spacecraft, a laser beam fired by extraterrestrials in an attempt to communicate with the earthlings, and an early experiment in nuclear physics which got out of hand. Numerous websites, conspiracy theories and sensational TV documentaries on the Fireball abound. In a fast-moving and non-technical narrative The Tunguska Fireball discusses all theories and then analyses the evidence to point an accusing finger at a prime suspect.