What was J.R.R. Tolkien’s final published Middle-earth book during his lifetime?

The Road Goes Ever On was J.R.R. Tolkien’s final published Middle-earth book during his lifetime.

The Road Goes Ever On: A Song Cycle was first published in 1967. It combines Tolkien’s poems and texts from Middle-earth with music by Donald Swann. Tolkien supplied linguistic and pronunciation notes, while Swann composed settings for the poems.

The book is unusual among Tolkien’s publications because it is a song cycle rather than a narrative novel. Its contents include songs associated with The Lord of the Rings, and the volume presents Middle-earth material in a form intended for performance.

Tolkien died in 1973. Several important books appeared after his death, including The Silmarillion in 1977 and Unfinished Tales in 1980. Those posthumous publications are therefore not the final Middle-earth book he personally saw published, even though they contain much more extensive lore.