COS-B was an ESA (European Space Agency) mission that, together with NASA's SAS-2, provided the first detailed views of the Universe in gamma rays. COS-B carried a single large experiment, the Gamma-Ray Telescope, which was the responsibility of a group of European research laboratories know as the Caravane Collaboration. Although originally projected to last two years, the spacecraft operated successfully for more than six, providing the first complete map of the Galaxy in the 2 keV-5 GeV energy range and identifying about 25 discrete sources.