The Book of Wonder is the seventh book and fifth original short story collection of Irish fantasy writer Lord Dunsany, considered a major influence on the work of J. R. R. Tolkien, H. P. Lovecraft, Ursula K. Le Guin, and others.

Lord Dunsany employed the talents of Sidney Sime to illustrate his fantasy short story collections, but The Book of Wonder is unique in that Sime drew the illustrations first, and Lord Dunsany wrote the tales to incorporate them: 'I found Mr Sime one day, in his strange house at Worplesdon, complaining that editors did not offer him very suitable subjects for illustration; so I said: "Why not do any pictures you like, and I will write stories explaining them, which may add a little to their mystery?

[2] The short story "How Nuth Would Have Practised His Art upon the Gnoles" is likely the origin of the term gnoll, used in a number of later works, notably the Dungeons and Dragons gaming franchise, to describe a humanoid fantasy race.

He described the main character of Dunsany's previous stories as Time, and his world as "curiously elementary", full of simple and terrible happenings.

However, he noted that though the new stories in The Book of Wonder were less marvellous, they were more closely related to the real world and more psychologically complex.