The Physiologus is the ancestor of the bestiary, a collection of chapters describing animal qualities and behaviours, usually with an allegorical meaning, which proliferated especially in England in the late Middle Ages. While much scholarly attention has been directed to the bestiary, the history of the transmission of the Physiologus has hardly been investigated. Evidence of the circulation of this treatise in the early medieval period is certainly scanty, since only two brief versions dating from this period have been preserved, one in Old English and another one in Latin. However, this monograph shows further proof of the knowledge of the Physiologus in Anglo-Saxon England. It also reveals the relationship of the only two surviving texts and their connection to the main Continental recension of the time. This study therefore demonstrates that the popularity of bestiaries in the later Middle Ages was largely due to the prominence that its predecessor, the Physiologus, enjoyed in the preceding period.