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. It was first published in hardcover by William Heinemann in November, 1912, and has been reprinted a number of times since. A 1918 edition from the Modern Library was actually a combined edition with Time and the Gods.

The book collects fourteen fantasy short stories by the author.

Lord Dunsany employed the talents of Sidney Sime to illustrate his fantasy short story collections, but The Book of Wonder is unique in that Sydney 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?"'

Of the 14 tales, only the last two ("Chu-Bu and Sheemish" and "The Wonderful Window") were not derived from a Sime drawing.

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.