In J. R. R. Tolkien's fictional Middle-earth, Ithilien is a region and fiefdom of Gondor.

Ithilien, or Moon-land, was the only part of Gondor which lay across the Great River Anduin, wedged in between the river and the Ephel Dúath of Mordor.

It was a fair and prosperous land during the Second Age and the first part of the Third Age, when Gondor was strong and Mordor deserted. Of old its chief city was Minas Ithil, but when this was captured by Mordor it was renamed Minas Morgul. After this the majority of its people fled across the Anduin to escape war, but the Stewards of Gondor still kept scouts in Ithilien, based on secret locations such as Henneth Annûn.

Ithilien was further divided in North and South Ithilien, but South Ithilien like Harondor was a contested area between Gondor and Near Harad.

In The Lord of the Rings, Gollum leads Frodo Baggins and Samwise Gamgee through Ithilien on the way to the pass of Cirith Ungol into Mordor. After witnessing a battle with Southrons of Harad accompanied by Oliphaunts, the hobbits are found by Faramir, the son of the Steward Denethor, but are allowed to continue when he is satisfied they are not agents of Sauron.

During the Fourth Age, Ithilien was ruled by the Princes of Ithilien, a line that started with Faramir. Minas Morgul was not repopulated, and Faramir ruled as Lord of the Emyn Arnen.