These books are a rare find from the Metropolitan Opera Guild, published by Grosset & Dunlap in 1938. They are a hardcover edition of Four Books of the Opera. The books are illustrated and authorized by the Metropolitan Opera Guild, making them a valuable addition to any collection. The content is in English and is suitable for children who are interested in learning about different operas. The books cover various topics, including Carmen, Aida, Lohengrin, & Hansel and Greek.