This book explores the relations between humans and other animals as they appear to a reader of medieval bestiaries, given that almost all of them are realized as parchment books and that parchment, although made from animal skin, looks much like human skin. Using Didier Anzieu’s concept of the Skin Ego and a theory of reading as assuming a second skin, the book explores how a supposedly human identity can be challenged by a reading process that inserts the reader into an animal skin. It examines the treatment of bestiary creatures in relation to the pages on which their entries are copied, showing how bestiarists’ teachings may be confirmed or undermined by the interaction between a text’s content, which is often focused on animals’ skins, their illustrations, which often outline or highlight those skins, and its material support, an actual instance of skin. The pages of many different manuscripts, transmitting numerous bestiary versions, are read closely in order to bring out possible interconnections between word, image, and parchment. Each chapter addresses an aspect of human-animal relations that is thematized both by medieval bestiaries and by modern theorists of the posthuman such as Giorgio Agamben and Jacques Derrida. In-depth coverage of Latin and French bestiary versions produces a new overall account of the development of the Physiologus tradition in Western Europe, one which attributes more importance to Continental traditions than previous Anglophone scholarship.