J.R.R. Tolkien’s first published novel about Bilbo Baggins was The Hobbit, published in 1937. Its full title is The Hobbit, or There and Back Again, and it follows Bilbo’s journey with Thorin Oakenshield and a company of dwarves.
The book began as a children’s fantasy story, but Tolkien connected it to the mythology he had been developing for years. The discovery of the One Ring during Bilbo’s encounter with Gollum became an important bridge to The Lord of the Rings, although the Ring’s original role changed as Tolkien developed the later story.
The Hobbit is not Tolkien’s first written work set in his imagined world, and it was not published after The Lord of the Rings. The Silmarillion was assembled and published posthumously by Christopher Tolkien in 1977.