This volume presents a new critical edition of the Greek text of Historia Animalium, Aristotle's largest and least studied work, by one of the foremost scholars of Aristotle's biological works and their philosophical significance. This posthumous edition has been completed for publication, with its Introduction expanded and updated, by Allan Gotthelf in consultation with specialists on various aspects of the project. Based on a study of every surviving manuscript, this edition is a considerable advance on previous texts.