This monograph on the version of the Medusa, which has only recently been attributed to the hand of Caravaggio by the most respected experts, recounts the process of recognition of this masterpiece. Initially the similarity of the work to the better known version at the Uffizi in Florence and the analogous manufacture of the frame brought the attention of the experts to this other Medusa. The hypothesis that Caravaggio executed doubles, the high quality of the painting, and the reference to it by the contemporary poet Murtola led to the conviction that another version of the known Medusa existed. Confirmation of the hypothesis was provided by x-rays and new technologies, which revealed the painting's genesis and eventually supported the suggestion that this version was the original. Analysis of the painting followed the twin paths of the more traditional historical and stylistic research and the more modern approach that also makes use of technology. This masterpiece by Caravaggio was thus the object of dedicated research in which modern instrumentation supported and was combined with the study of archive documentation and the style in which the work was painted, thereby opening potentially new lines of research and a new way of looking at an artwork. The accounts of the experts are accompanied by illustrations and photographs of the highest order, enabling not only scholars but all art lovers the opportunity to appreciate and know this previously neglected work in full detail.