Tolkien’s The Lord of the Rings is made up of three books. They are The Fellowship of the Ring, The Two Towers, and The Return of the King.
Tolkien conceived the work as a single long novel, but its publisher issued it in three volumes because of practical and production considerations. The first volume appeared in 1954, and the second and third followed in 1954 and 1955. Each volume contains two internal books, making six numbered books in the story overall, plus appendices.
This creates a frequent counting confusion. The work is commonly called a trilogy because it was published in three volumes, while the internal structure contains six books. The Hobbit is a separate novel and is not one of the three volumes of The Lord of the Rings.