Video produced before the launch of ESA's Integral gamma-ray observatory, providing a brief history of gamma-ray astronomy. The existence of gamma rays was postulated long before they were actually discovered in the 1960s. Interview with Prof. Volker Schoenfelder at MPE, Garching, one of the pioneers of gamma-ray astronomy, who worked on Cos-B, ESA's first gamma-ray observatory. Launched in 1975, Cos-B kick-started Gamma-ray astronomy, providing the first complete map of the Galaxy in gamma rays. NASA's Compton Gamma Ray Observatory was launched in 1991, carrying 4 instruments. Interview with Francois Lebrun at CEA Saclay, member of a team that developed one of the instruments on Integral.