From the publisher's description: "The Legend of Sigurd and Gudrún is a previously unpublished work by J.R.R. Tolkien, written while Tolkien was Professor of Anglo-Saxon at Oxford during the 1920s and '30s, before he wrote The Hobbit and The Lord of the Rings. It makes available for the first time Tolkien’s extensive retelling in English narrative verse of the epic Norse tales of Sigurd the Völsung and The Fall of the Niflungs. It includes an introduction by J.R.R. Tolkien, drawn from one of his own lectures on Norse literature, with commentary and notes on the poems by Christopher Tolkien."
More info here on the book as well as the upcoming audio book narrated by Brian Cox:
HT: Gene Veith