Originally formed by Prince Federico Cesi in the early seventeenth century and later acquired by Cassiano, these drawings constitute the first truly scientific study of fossilized woods and are executed with such finesse, skill and detail that they will be of immense interest both to art-historians and to historians of science. The drawings, the majority of which have remained unstudied and unpublished until now, include specimens of wood and animal fossils, ammonites and concretions, pyrites and baked clays, as well as a series of field drawings giving the sites where these specimens were found. The introductory essays discuss the background to Cesi's project, together with the importance of the drawings to the history of seventeenth-century culture and science.