"Unfinished Tales of Númenor and Middle-Earth" is a posthumous collection of stories and essays by J.R.R. Tolkien, edited by his son Christopher Tolkien. The book includes various tales and fragments that were never fully completed by the author, as well as previously unpublished writings.

The book begins with a section called "The First Age," which includes stories such as "Of Tuor and his Coming to Gondolin," "Narn i Hîn Húrin," and "A Description of the Island of Númenor." These stories provide further depth to the mythology of Middle-Earth, including the fates of the elves and the rise and fall of Númenor.

The second section, "The Second Age," covers the history of the Rings of Power and the downfall of Sauron. This includes the story of Galadriel and Celeborn, as well as the history of the Palantiri, the seeing-stones that allowed communication over great distances. The section also includes an account of the War of the Last Alliance, which led to the defeat of Sauron and the destruction of the One Ring.

The final section of the book, "The Third Age," includes various unfinished tales and essays. These include "The Disaster of the Gladden Fields," which tells the story of the last stand of Isildur, and "Cirion and Eorl," which covers the history of the kingdom of Rohan. There are also essays on the history and culture of the dwarves, as well as notes on the geography of Middle-Earth.

Throughout the book, Christopher Tolkien provides commentary and notes on his father's writings, helping to shed light on the author's creative process and the evolution of his ideas. He also includes drafts and alternate versions of some of the stories, allowing readers to see how the author's ideas developed over time.

Overall, "Unfinished Tales of Númenor and Middle-Earth" offers a fascinating glimpse into the world-building and storytelling process of one of the most beloved authors of fantasy literature. While the stories may not be fully complete, they are still rich with detail and provide valuable insights into the history and mythology of Middle-Earth. For fans of J.R.R. Tolkien's work, this book is a must-read.