Which 1977 book edited by Christopher Tolkien was based on J.R.R. Tolkien’s mythology?

The 1977 book edited by Christopher Tolkien from J.R.R. Tolkien’s mythology was The Silmarillion.

The Silmarillion was published after Tolkien’s death, with Christopher Tolkien organizing and editing material that had been written and revised across many decades. It presents creation stories, the history of the Elves, the First Age wars, and the events that lead toward later ages of Middle-earth.

Unlike The Hobbit and The Lord of the Rings, it is not a single straightforward adventure novel. Its sections use different forms, including mythic narrative, historical account, and tragedy. Christopher Tolkien later published further studies of his father’s drafts, including Unfinished Tales and The History of Middle-earth.