The End of the Third Age is comprised of the first section of the hardcover volume published as Sauron Defeated, the ninth volume of The History of Middle-earth. It completes Christopher Tolkien's account of the creation of The Lord of the Rings begun in the earlier volumes, The Return of the Shadow, The Treason of Isengard, and The War of the Ring. [via]
The End of the Third Age begins with Sam's rescue of Frodo from the Tower of Kirith Ungol, and giving a very different account of the Scouring of the Shire, this part ends with versions of the hitherto unpublished Epilogue, in which, years after the departure of Bilbo and Frodo from the Grey Havens, Sam attempts to answer his children's questions.
The book is illustrated with changing conceptions of Kirith Ungol and Mount Doom, as well as previously unpublished drawings of Orthanc and Dunharrow.