Below is a summary of the contents in the twelve volumes of The History of Middle-earth series.
It is a part from the essay "Unfinished Tales and the History of Middle-earth: A Lifetime of Imagination" by Elizabeth A. Whittingham, from book A Companion to J.R.R. Tolkien (2014).
Summary
After Tolkien's death, his son Christopher sorted through his unpublished writings, organizing them largely chronologically, and after publishing The Silmarillion and Unfinished Tales, issued the 12 volumes of The History of Middle-earth between 1983 and 1996. The works in The History of Middle-earth include many versions of some stories in both prose and verse forms, and for the most part, the material is arranged in the order that they were written with detailed notes and commentary by Christopher. For example, Tolkien's creation myth first appears in The Book of Lost Tales I as "The Music of the Ainur", a text composed sometime in early 1919. Tolkien wrote another version of that myth in the mid-1930s, entitled "Ainulindalë", which is published in The Lost Road and Other Writings. A final version of the "Ainulindalë" completed during the years 1948–1951 is printed in Morgoth's Ring. This latest version is the one on which Christopher based the creation story in the 1977 Silmarillion. Besides such revisions over the years, there are also examples of multiple versions of tales written within a short period of time. For example, during the late 1930s, the "Quenta Silmarillion" was composed in four different stages (A, B, C, and D) and in longer and shorter versions, QS I and QS II, respectively.
The Book of Lost Tales I (1983) and II (1984)
These first two volumes of The History of Middle-earth series cover primarily the same time period of Tolkien's writing, the stories being arranged in accordance with the overall exposition of The Silmarillion. In 1914, he first pens the poem "The Voyage of Éarendel the Evening Star," which "is the germ from which the mythology evolved" and a later version of which is found in Book II; however, most of the stories were written between 1916 and 1919. These early versions of the stories that appear in revised form in The Silmarillion have many interesting elements missing from the 1977 text. The stories are set in the framework of a larger story: Eriol, a traveler, comes to the Cottage of Lost Play on the Lonely Island, Tol Eressëa. While he visits there, he hears the lost tales, mainly related by various Eldar in the Room of the Log Fire; the links that connect the various stories include characters and circumstances that were eliminated from the later works when the framework was abandoned. In these early tales, many names and details differ from their later forms. Eriol is told about the creation of the universe in "The Music of the Ainur", a tale that already contains most of the elements of the later "Ainulindalë". "The Coming of the Valar and the Building of Valinor" introduces the Valar and the array of lesser spirits that enter the world and describes the spectacular palaces built by Aulë for his fellow divinities, though these fanciful dwellings disappear from later versions. Within the pages of this tale is also an early visual representation of Arda's cosmology, fashioned like a ship. "The Tale of the Sun and Moon" explains how the ships that bore the Sun and Moon came to be built and set in the heavens and includes an early published version of the poem, "Why the Man in the Moon Came Down Too Soon." Attached to the Sun and Moon, according to "The Hiding of Valinor", are heavy cables and slender cords that measure the years as time passes. Book I concludes with "Gilfanon's Tale," a brief account of Tû the Wizard and Nuin, the Dark Elf.
Book II contains intriguing tales from this early period: "The Tale of Tinúviel," "Turambar and the Foalókë," and "The Nauglafring." The story about Tinúviel is different from later versions in that Beren's name is left out of the title, and he is also one of the Eldar. As a result of this difference in status, much of Beren's background and the tensions between Beren and Lúthien's father because he is a mortal are altered or missing. There is no great wolf guarding Melko's gates and no reference to Sauron, but instead Tevildo Prince of Cats occupies great halls, and Melko gives Beren into the great cat's keeping. In "Turambar and the Foalókë," certain elements found in later versions are missing, such as Túrin's involvement with Mîm and the Pettydwarves, but this early tale includes a conversation between Mavwin/Morwen and Glorund/Glaurung that is later omitted. Túrin's parents are admitted into the halls of Mandos, a fate denied all Men in future versions, and initially Túrin and his sister are rejected because of their incest. "The Fall of Gondolin," the first tale to be written, is fully developed and in a form that already contains many elements of the final version.
The Lays of Beleriand (1985)
The third volume of the series contains primarily verse works from the 1920s. The two major works are "The Lay of the Children of Húrin," written in alliterative verse, and "The Lay of Leithian." "The Lay of the Children of Húrin" explores the early events in the lives of Húrin and his children, Túrin Turambar, and Nienor/Níniel; the alliterative form seems well suited to these dark episodes in their family history and is particularly effective in the dialogue between Húrin and Morgoth. "The Lay of Leithian," which relates the story of Beren and Lúthien, provides one of many versions of that tale. Among poems that were set aside after only limited development are The Flight of the Noldoli from Valinor, a fragment of an alliterative Lay of Eärendel, and The Lay of the Fall of Gondolin. Readers of Humphrey Carpenter's 1977 authorized biography, aware of the humorous commentary by C.S. Lewis concerning "The Lay of Leithian," can now read the scholarly examination of the poem voiced by Peabody, Pumpernickel, and Bentley.
The Shaping of Middle-earth (1986)
The fourth volume of the series contains works primarily from the early 1930s. Besides a few annals, the one major work, the "Quenta Noldorinwa," is the only complete version of the "Silmarillion" ever finished by Tolkien. It is also the version of the "Silmarillion" that was in existence when Tolkien was writing The Hobbit. The annals divide the material into two sections: "The Annals of Valinor," which covers the time in Valinor before the awakening of the Elves and while the Eldar dwelt in the Undying Lands, and "The Annals of Beleriand," which covers the events in Beleriand and the war between Melkor and Elves and Men during the First Age. This collection also contains early maps and "The Ambarkanta," a description of the cosmology of the lands and universe of Middle-earth as conceived by Tolkien during the early 1930s.
The Lost Road and Other Writings (1987)
The fifth volume of the series contains works from the mid-to-late 1930s, including later versions of the annals and the last version of the "Silmarillion" before Tolkien began writing The Lord of the Rings. "The Fall of Númenor" and "The Lost Road" include references to Tolkien's recurring Atlantis dream. "The Fall of Númenor" is fully set in Middle-earth and later evolves into the "Akallabêth" in The Silmarillion. Though brief, it is the earliest account of Númenor and the Edain during the Second Age. "The Lost Road," a tale of time-travel, is the result of the agreement between Tolkien and C.S. Lewis to write stories that they would enjoy and connects the Primary World in the twentieth century to Tolkien's Secondary World, Middle-earth, through Númenor. Etymological works also comprise a significant portion of the book.
The Return of the Shadow (1988)
In the sixth volume of the series, the beginning of The Lord of the Rings emerges in its various versions. The work, begun in December of 1937, continued through the next two years and tracks the Hobbits and their companions as far as the Mines of Moria. These early versions and numerous rewritings focus on events in the Shire and on Tolkien's first concepts of the Ring's history. These accounts contain many elements that never survived into the tale's final form: Bingo Baggins instead of Frodo, Odo as a companion on the journey instead of Sam, and Trotter the Hobbit as a precursor to Strider the Dúnadan. This last aspect grew out of the idea suggested in The Hobbit that from time to time Gandalf had spirited away young Hobbit boys and girls on adventures. Reading these early concepts and seeing the tales evolve are intriguing for those who appreciate the published The Lord of the Rings.
The Treason of Isengard (1989)
The seventh volume of the series includes continuing revisions of early sections of The Lord of the Rings as well as further development of the story beyond the Mines of Moria. As in the previous volume, many characters and events from these writings disappear or take on completely different incarnations in Tolkien's revisions: Hamilcar Bolger, Tarkil the Dúnadan, Saramund the Grey, Treebeard the evil giant, and Gandalf's rescue of Hamilcar from the Black Riders on his swift horse Galeroc. Also included is the tale as it progresses, describing the journey of the company from the Mines of Moria, through Lothlórien, down the Great River to the breaking of the Fellowship. In the final section are chapters on the Riders of Rohan, the Uruk-Hai, Treebeard the Ent – no longer a fell foe – and other elements that eventually appeared in The Two Towers.
The War of the Ring (1990)
The story of the war against Sauron continues in the eighth volume of the series and contains material from 1942, before the break from writing that Tolkien took during 1943 and 1944, and the material he wrote after his return. The text picks up with the journey from Edoras to Helm's Deep and continues through a chapter in which Gandalf contemplates the significance of the palantír, Pippin's involvement eventually being included. The second section of this volume takes up with Frodo and Sam trying to find their way into Mordor, which was begun in the spring of 1944 and continues through the carrying away of Frodo's body into the tower of Kirith Ungol. The third section begins with Gandalf's and Pippin's arrival in Minas Tirith, "The Muster of Rohan," "The Siege of Gondor," and subsequent events through to and including the opening of the Black Gate. Though there are fewer major differences between these early versions and the published text, a few significant differences are evident: Faramir is originally named Falborn; Éowyn dies in the attack by the Witch King of the Nazgûl; there are many spiders instead of only Shelob in Kirith Ungol; and the projected ending tells of Sam wrapping up many loose ends for the reader by reading to his children from his book.
Sauron Defeated (1992)
The ninth volume of the series includes texts largely from the mid-1940s, beginning with the final chapters of The Lord of the Rings in their preliminary form, which picks up with Frodo and Sam in Mordor. In these chapters, the original Sharkey was not Saruman but Cosimo Sackville-Baggins – later named Lotho – and Frodo is lively, aggressive, and determined, unlike the weary, wounded character of the published text. The most interesting difference is an Epilogue, similar to the one previously anticipated, that focuses on Sam and his numerous children and provides an opportunity to inform the reader about the future adventures of the members of the Fellowship. Also included in the ninth volume are the intriguing "Notion Club Papers," the minutes of a group similar to the Inklings, of which Tolkien was a member. This tale, which is one of the treasures of the entire series, presents the mysteries found in the twenty-first century among discarded papers. "The Drowning of Anadûnê," the third section of the book, is a later version of "The Fall of Númenor," surprising in the major alterations and deletions made to the earlier text. Christopher Tolkien attributes these changes to the amount of time that had elapsed since the writing of the previous version and the growing significance of Númenor as The Lord of the Rings developed.
Morgoth's Ring (1993)
The series' tenth volume has the most intriguing title of all the books: Morgoth has, in the creation process, put himself and his discordant elements into the universe, and the World, corrupted from creation, is Morgoth's Ring. Just as Sauron cannot fully be destroyed while the One Ring exists, the Dark Lord cannot be destroyed while the World exists. This volume contains many works that resulted from the popularity of The Lord of the Rings. Following the book's publication in 1954 and 1955, Tolkien was inundated with questions from readers about his characters and their world, which resulted in much of Tolkien's writing in the late 1950s as he considered those questions. Consequently, this volume contains details concerning the lives of Elves, reincarnation, and body/spirit relationships for both Elves and Men. The story of "Finwë & Míriel" includes a debate among the Valar, and the conversation in the "Athrabeth Finrod Ah Andreth" centers on the metaphysical differences between Elves and Men, a philosophical discussion with a personal slant. The book also incorporates versions of the "Silmarillion" from both the early and late 1950s, as well as a final section entitled "Myths Transformed" that contains some interesting notes on cosmology, Melkor, Orcs, and Aman.
The War of the Jewels (1994)
In the eleventh volume, the "Silmarillion" of the 1950s continues. Also included are a number of significant texts such as "The Grey Annals," a revision of "The Annals of Beleriand," and "The Later Quenta Silmarillion." "Quendi and Eldar" is a significant linguistic work, and "The Tale of Years" is useful for understanding the chronology of the later Elder Days. Among this volume's most interesting texts are stories and notes about Húrin, Ælfwine, Maeglin, and the Ents and Eagles. The most fully developed of these texts, "The Wanderings of Húrin," describes the release of Húrin from Angband following 28 years of captivity, and his journeys, that include an attack on the Easterlings of Hithlum, his gathering of men around him, the sorrowful reunion with Morwen just before her death, and his trial by the Haladin. The chapter "Maeglin" examines variations and expansions of the text that appears in The Silmarillion.
The Peoples of Middle-earth (1996)
Most of the twelfth volume focuses on the last of The Lord of the Rings writings, in particular, Tolkien's preliminary work on the Appendices. The rest of the book brings together short pieces generally from the last years of Tolkien's life. "Of Dwarves and Men" reflects on the Book of Mazarbul and informs about the Longbeard Dwarves. "The Shibboleth of Fëanor," "The Problem of Ros," and "Dangweth Pengoloð" are linguistic in focus but include various facts about the family of Finwë and the lives of Elves and Men. "Last Writings," from the last year of the author's life, tells briefly of "The Five Wizards," "Círdan," and "Glorfindel," Tolkien's one example of a reincarnated Elf. Another short piece, "Of Lembas," explains that waybread came from the Valar and is followed by two noteworthy unfinished works. "The New Shadow" picks up a century after the events of The Lord of the Rings and looks ahead into the Fourth Age and what happens after Aragorn's reign ends. "Tal-Elmar" describes the Second Age arrival of Númenóreans in Middle-earth from the perspective of those who already live there.
Conclusion
The 12 volumes of The History of Middle-earth undoubtedly represent the prolific nature of Tolkien's writing throughout his life and contain some wonderful treasures. Different people will be attracted by varying works, and some may see the volumes as an interesting resource for information, while others will want to read piecemeal, picking through to choose only favorite tidbits, and a few will want to devour them in their entirety – a feast to be savored over an extended period of time. One of the many pleasures of enjoying all these books is to observe the evolution of individual tales over many decades of the author's life.