Inspiring discovery through free access to biodiversity knowledge.
The Biodiversity Heritage Library improves research methodology by collaboratively making biodiversity literature openly available to the world as part of a global biodiversity community.
This site is the result of collaboration between many different natural history and botanical libraries, in conjunction with the Internet Archive. While you might think this is only going to help researchers of plants and animals, there are other medieval resources as well.
You can search by title, author, date, collection or contributor. You can also download the books in several different formats.