Otia Imperialia is an early 13th-century encyclopedic work, the best known work of Gervase of Tilbury. It is an example of speculum literature. Also known as the "Book of Marvels", it primarily concerns the three fields of history, geography, and physics, but its credibility has been questioned by numerous scholars including philosopher Gottfried Leibniz, who was alerted to the fact that it contains many mythical stories. Its manner of writing is perhaps because the work was written to provide entertainment to Holy Roman Emperor Otto IV. However, many scholars consider it a very important work in that it "recognizes the correctness of the papal claims in the conflict between Church and Empire." It was written between 1210 and 1214, although some give the dates as between 1209 and 1214 and numerous authors state it was published c.1211. These earlier dates must be questioned, however, as the Otia contains stories that take place in 1211 and later. S. E. Banks and James W. Binns, editors and translators of what is considered to be the definitive version of the Otia, suggest that the work was completed in the last years of Otto IV's life, saying "it seems most likely [...] that the work was sent to Otto sometime in 1215", due to the inclusion of the death of William the Lion, King of Scotland, which took place in 1214, and the fact that King John was still living while it was written; John died in 1216.

Gervase of Tilbury was an English canon lawyer, statesman and cleric. He enjoyed the favour of Henry II of England and later of Henry's grandson, Emperor Otto IV, for whom he wrote his best known work, the Otia Imperialia.