Which Tolkien book was published posthumously in 2017 about Beren and Lúthien?

Beren and Lúthien was published posthumously in 2017 as a standalone Tolkien book about the legendary mortal Beren and the Elf Lúthien.

Christopher Tolkien edited the volume, which brings together versions of the story written across different periods of J.R.R. Tolkien’s career. The tale appears in several forms, including prose and verse, rather than as one newly completed novel. Tolkien’s illustrations are also included in the book.

The story is one of the central romances of Tolkien’s mythology. Beren and Lúthien undertake a perilous quest involving a Silmaril, one of the great jewels made by Fëanor. Their story is connected to the history of the First Age and is also echoed in Tolkien’s own life: the names “Beren” and “Lúthien” appear on the gravestone shared by Tolkien and his wife, Edith.