A wide ranging overview of Unicorns in literature from 2600 BC to the modern day.
Basically, Chris Lavers examines which real animals may have inspired the totemic figure of the Unicorn, and which provided the Unicorn horns that were a valued commodity in 16th Century Europe, and also examines the importance of the Unicorn in religious belief and art.
This is a fascinating subject, which Lavers brings to life with accessible and clear prose. I'm not sure why he doesn't identify the Indian Rhino more definately as the source for the Unicorn; When repeating the ancient descriptions of the Manticore, he is happy to identify this with a distorted account of the Tiger. Personally, I would feel if any wild animal inspired travellers' accounts of Unicorns, the one horned Rhino must fit the bill.
Other arguments, e.g. the true identity of the Biblical Unicorn, a.k.a the Reem, or the possibility that ancient cultures "made" one horned farm animals were very convincing.
The description of the discovery of the Okapi is slightly tenuously linked to the subject but it's a great story that deserves to be re-told. And Okapis are ace.