Historia animalium: In ten books. 48 editions

The Historiae animalium was Gesner's magnum opus, and was the most widely read of all the Renaissance natural histories. The work was so popular that Gesner's abridgement, Thierbuch ("Animal Book"), was published in Zurich in 1563, and in England Edward Topsell translated and condensed it as a Historie of foure-footed beastes (London: William Jaggard, 1607). Gesner’s monumental work is a record that attempts to build a connection between the ancient knowledge of the animal world and modern science. He then adds his own observations to formulate an all-inclusive description of the natural history of animals.
Gesner’s Historiae animalium is based on the Old Testament, Hebrew, Greek, and Latin sources. The encyclopedic work is a compilation from folklore and ancient and medieval texts. The work compiled the inherited knowledge of ancient naturalists like Aristotle, Pliny and Aelian. Gesner was known as "the Swiss Pliny."For information on mythical animals he relied heavily on the material from the Physiologus. His research style was based on four principles: observation, dissection, travel, and an accurate description of the animals. These viewpoints from actual experience were new to Renaissance scholars. They had usually depended on information obtained solely on previous Classical authors for their reference material.
Though in his large work Gesner sought to distinguish facts from myths, his encyclopedic work also included mythical creatures and imaginary beasts, intermixed with the strange newly discovered animals of the East Indies, those of the far north and animals brought back from the New World. The work included extensive information on mammals, birds, fish, and reptiles. It described in detail their daily habits and movements. It also included their uses in medicine and nutrition. Historiae animalium showed the animals' places in history, literature and art. Sections of each chapter detailed the animal and its attributes, in the tradition of the emblem book. Gesner's work included facts in different languages such as the names of the animals. His information drew from folktales, myths, and legends. The colored woodcut illustrations were the first real attempts to represent animals in their natural environment. It is the first book with fossil illustrations.
Gesner acknowledges one of his main illustrators was Lucas Schan, an artist from Strasbourg. He likely used other illustrators as well as himself. Gesner's approach to natural history was unusual for sixteenth century readers - it contained illustrations and pictures.
The first volume is an illustrated work on live-bearing four-footed animals. Volume 2 is on egg-laying quadrupeds. Volume 3 is on birds. Volume 4 is on fish and aquatic animals. A fifth volume, on snakes and scorpions, was published in 1587, after Gesner’s death.
There was extreme religious tension at the time Historiae animalium came out. Under Pope Paul IV it was felt that the religious convictions of an author contaminated all his writings,[4] so it was added to the Catholic Church's list of prohibited books. Gesner was Protestant.