The geography of Middle-earth encompasses the physical, political, and moral geography of J. R. R. Tolkien's fictional continent Middle-earth on the planet Arda, but widely taken to mean all of creation (Eä) as well as all of his writings about it. Arda was created as a flat world, incorporating a Western continent, Aman, which became the home of the godlike Valar, as well as Middle-earth. At the end of the First Age, the Western part of Middle-earth, Beleriand, was drowned in the War of Wrath. In the Second Age, a large island, Númenor, was created in the Great Sea, Belegaer, between Aman and Middle-earth; it was destroyed in a cataclysm near the end of the Second Age, in which Arda was remade as a spherical world, and Aman was removed so that Men could not reach it.

In The Lord of the Rings, Middle-earth at the end of the Third Age is described as having free peoples, namely Men, Hobbits, Elves, and Dwarves in the West, opposed to peoples under the control of the Dark Lord Sauron in the East. Some commentators have seen this as implying a moral geography of Middle-earth. Tolkien scholars have traced many features of Middle-earth to literary sources such as Beowulf, the Poetic Edda, or the mythical Myrkviðr. They have in addition suggested real-world places such as Venice, Rome, and Constantinople/Byzantium as analogues of places in Middle-earth. The cartographer Karen Wynn Fonstad has created detailed thematic maps for Tolkien's major Middle-earth books, The Hobbit, The Lord of the Rings, and The Silmarillion.

Tolkien's Middle-earth was part of his created world of Arda. It was a flat world surrounded by ocean. It included the Undying Lands of Aman and Eressëa, which were all part of the wider creation, Eä. Aman and Middle-earth were separated from each other by the Great Sea Belegaer, analogous to the Atlantic Ocean. The western continent, Aman, was the home of the Valar, and the Elves called the Eldar. Initially, the western part of Middle-earth was the subcontinent Beleriand; it was engulfed by the ocean at the end of the First Age. Ossë, on behalf of the Valar, then raised the island continent of Númenor as a gift to the now homeless Men of Beleriand, thenceforth called Númenóreans.

After Eru Ilúvatar destroyed Númenor near the end of the Second Age, he remade Arda as a round world, and the Undying Lands were removed from Arda so that Men could not reach them. The Elves could go there only by the Straight Road and in ships capable of passing out of the sphere of the earth. Tolkien then equated Arda, consisting of both Middle-earth's planet and the heavenly Aman, with the Solar System, the Sun and Moon being celestial objects in their own right, no longer orbiting the Earth.

The extreme west of Middle-earth in the First Age was Beleriand. It and Eriador were separated from much of the south of Middle-earth by the Great Gulf. Beleriand was largely destroyed in the cataclysm of the War of Wrath, leaving only a remnant coastal plain, Lindon, just to the west of the Ered Luin (also called Ered Lindon or Blue Mountains). The cataclysm divided Ered Luin and Lindon by the newly created Gulf of Lune; the northern part was Forlindon, the southern Harlindon.

In the northwest of Middle-earth, Eriador was the region between the Ered Luin and the Misty Mountains. Early in the Third Age, the northern kingdom of Arnor founded by Elendil occupied a large part of the region. After its collapse, much of Eriador became wild; regions such as Minhiriath, on the coast south of the River Baranduin (Brandywine), were abandoned. A small part of the region was occupied by Hobbits to form the Shire. To the northwest lay Lake Evendim, once called Nenuial by the Elves. A remnant of the ancient forest of Eriador survived throughout the Third Age just to the east of the Shire as the Old Forest, the domain of Tom Bombadil. Northeast of there is Bree, the only place where hobbits and Men live in the same villages. Further east from Bree is the hill of Weathertop with the ancient fortress of Amon Sûl, and then Rivendell, the home of Elrond. South from there is the ancient land of Hollin, once the elvish land of Eregion, where the Rings of Power were forged. At the Grey Havens (Mithlond), on the Gulf of Lune, Círdan built the ships in which the Elves departed from Middle-earth to Valinor.

The Misty Mountains were thrown up by the Dark Lord Melkor in the First Age to impede Oromë, one of the Valar, who often rode across Middle-earth hunting. The Dwarf-realm of Moria was built in the First Age beneath the midpoint of the mountain range. The two major passes across the mountains were the High Pass or Pass of Imladris near Rivendell, with a higher and a lower route, and the all-year Redhorn Pass further south near Moria.

East of the Misty Mountains, Anduin, the Great River, flows southwards, with the forest of Mirkwood to its east. On its west bank opposite the southern end of Mirkwood is the Elvish land of Lothlorien. Further south, backing on to the Misty Mountains, lies the forest of Fangorn, home of the tree-giants, the ents. In a valley at the southern end of the Misty Mountains is Isengard, home to the wizard Saruman.