J.R.R. Tolkien sold the film and merchandising rights for The Hobbit to United Artists in 1966. At some point afterward, United Artists in turn sold the rights and Saul Zaentz eventually acquired them. Zaentz set up Tolkien Enterprises, a division of the Saul Zaentz Company, in 1977 to administer the rights for both The Hobbit and The Lord of the Rings. All film, radio, stage, and television adaptations since that time appear to have been licensed from Tolkien Enterprises.
MGM/United Artists apparently owns the distribution rights for "The Hobbit". It has been alleged that a script for The Hobbit has been circulating at MGM/UA but they are not moving forward with the project because they do not own production rights.
It 1998 it was reported to Xenite.Org that the Saul Zaentz Production Company was working on a "Hobbit" project. That project has since been shelved, and New Line Cinema may have a right of first refusal on producing a "Hobbit" movie after Peter Jackson's "The Lord of the Rings" movies are completed.