This essay takes a material culture approach to the fate of the unicorn, that ultimate symbol of irrationality and credulity, in the natural history collection of the age of Enlightenment. Exploring the interplay between unicorn horns, narwhals, rhinos and other kinds of horn present in the eighteenth-century French collection, it shows that in fact unicorns never disappeared from the cabinet, but rather presided over new narratives of what Enlightenment was about. Further, it argues that this change in the status of unicorns was associated with changing patterns of the global whaling industry, which made narwhal horns widely available to Europeans, and the narwhal into a natural historical object. What real objects could, or could not, be represented in the collection as specimens had an important bearing upon the credibility of animal kinds outside the space of the cabinet, yet within that space, the juxtaposition and financial value of specimens produced important narratives of the relationship between horn specimens and natural species like rhinos and narwhals existing in the real world—species which never completely shed their fictive character, like the unicorn itself.