The lands to the east of the Great Sea; also called the Hither Lands, the Outer Lands, the Great Lands, and Endor.
The Mortal Lands of Arda.
The great continent on which much of the Silmarillion, and the adventures of The Hobbit and The Lord of the Rings, are set. Little is known of the East and South of Middle-earth, or of the far north, but the geography and history of its Western lands are chronicled in great detail.
Ancient Times: The foundations of Middle-earth were laid by Aulë in times ancient beyond reckoning, and the Valar lit the new lands with two great Lamps, Illuin in the north and Ormal in the south. From fear of Tulkas, Melkor had fled beyond the Walls of the World, and Middle-earth was a place of peace and beauty. The Valar themselves dwelt in its central regions, on the green island of Almaren. This was the time known as the Spring of Arda.
Unknown to the Valar, though, Melkor secretly returned, and delved his first great fortress of Utumno in the mountains of the far distant north. When he judged the time was right, he assailed Almaren and, surprising the Valar, destroyed their habitation in Middle-earth. Fleeing back to Utumno, he saved himself from the wrath of Tulkas. This is one of the great disasters of Middle-earth's history: the Valar departed forever, and left Middle-earth under the sole control of Melkor, who claimed it as his own.
Though the Valar made a new home for themselves in Aman, and lit their new land of Valinor with the light of the Two Trees, Middle-earth was now left in darkness for many Ages. The Valar did not completely forget their ancient home, though, and Yavanna and Oromë, especially, came there from time to time to try and mend the hurts of Melkor if they could.
It was at this time, too, that Aulë returned, and secretly fashioned a hall beneath the mountains of Middle-earth. It was there that he wrought the Seven Fathers of the Dwarves, who were given life by Ilúvatar, and set to sleep until the awakening of the Firstborn.
Despite these brief visits from the Valar, though, Middle-earth was effectively controlled by Melkor, who was free to act as he would. Slowly, his polluted realm spread southwards over Middle-earth.
The Coming of the Elves: The Awakening of the Elves at Cuiviénen brought about profound changes in Middle-earth. At first they lived in darkness, prey to the creatures of Melkor, but Oromë found them, and the Valar decided to act: they went to war against Melkor.
There followed the Battle of the Powers, in the north and west of Middle-earth. That war rent and twisted the lands, giving them the shape they were to keep until the War of Wrath at the end of the First Age. Dorthonion and the highlands north of Beleriand were raised up at that time, and many bays, including the Bay of Balar, were created.
Melkor was ultimately defeated, and taken as a prisoner back to Valinor. After much debate, the Valar also offered the Elves a home in Aman, and many accepted. Led by Oromë, the Vanyar, Noldor and Teleri made the Great Journey across Middle-earth from the far east where they awoke to its western shores.
Many of these departed Middle-earth across the Sea, but some remained, of which the major groups were the Sindar of Beleriand and the Nandor of the Anduin valley. Other groups, mainly of Telerin origin, had also left the Journey: these were the people who were to become known as the Silvan Elves. Also, in the far east, remained the Elves who had refused the summons of the Valar, the Avari. All these kinds together are known as the Moriquendi, the Dark Elves, for they did not go to Valinor or see the light of the Two Trees.