The Nature of Middle-Earth is a posthumous work by J.R.R. Tolkien, edited by Carl F. Hostetter, that explores and delves into the complex and lesser-known aspects of Middle-earth, the fictional world from The Lord of the Rings and The Silmarillion. This book presents a compilation of Tolkien's writings on the nature of time, the existence of Elves, the immortality of the Valar, and various other philosophical and metaphysical concepts within Middle-earth. It also sheds light on Tolkien's intricate creation of languages, cosmology, and the evolving nature of the world he crafted. These writings, which were previously unpublished or scattered across different sources, offer a deeper understanding of the underlying themes and ideas in Tolkien's world-building. The Nature of Middle-Earth provides scholars and fans alike with a rare glimpse into Tolkien’s thoughts and the elaborate mechanics of the universe he created.