Caricature emerged as a pictorial genre in early modern Italy and became a potent form of social satire practiced by the period's foremost draftsmen, including the Carracci and Guercino. The deformed and misshapen subjects of caricature drawings coincided with a fascination with monstrosity. Monsters, aberrations, and anomalies reflected a cultural appreciation for the curious. The monster that slowly took shape in scientific literature was first alluded to in comparative physiognomic texts that related human to beast, then made brief appearances in the discourse on medical conditions, and finally became the primary focus of specialty publications. The attention given to physical aberrance led to the birth of teratology, the medical study of abnormal development, and the subsequent publication of several well-known monster histories by Fortunio Liceti and Ulisse Aldrovandi. This essay considers the rise of the monstrous by examining several trends in contemporary scientific discourse: the vogue for comparative physiognomy, the investigation of anatomical abnormalities, the rise of monster literature, and the transmission of monstrosity in popular culture. Scholars have long explored the use of anatomical studies by Renaissance artists. The essay expands on this research to suggest that artists were aware of medical advances that investigated the conditions of healthy as well as diseased bodies. Liceti's and Aldrovandi's histories demonstrate a change in the status of the monster—from freak omen to marvelous creature of nature—revealing the naturalization of the beast in the sciences. Lastly, monster phenomena were disseminated beyond the elite science of scholarly Latin publications through a variety of media, including pamphlets and broadsides in the vernacular. These publications were rich with visual material that begs comparison with caricature drawings.