The Lord of the Rings is an epic high fantasy novel written by the English academic and philologist J. R. R Tolkien. The story began as a sequel to Tolkien's earlier work, The Hobbit, but developed into a much larger story. It was written in stages between 1937 and 1949, with much of it being created during World War II. Although intended as a single-volume work, it was originally published in three volumes in 1954 and 1955, and it is in this three-volume form that it is popularly known. It has since been reprinted numerous times and translated into many different languages, becoming one of the most popular and influential works in 20th-century literature.

The story of The Lord of the Rings takes place in an alternate pre-history, the Third Age of Middle-earth. The lands of Middle-earth are populated by Men (humans) and other humanoid races (Hobbits, Elves, Dwarves, and Orcs), as well as many other creatures, both real and fantastic (Ents, Wargs, Balrogs, Trolls, etc.). The story centres on the Ring of Power made by the Dark Lord Sauron in an earlier age. From quiet beginnings in the Shire the story ranges across Middle-earth following the course of the War of the Ring through the eyes of its characters, most notably the hobbits, Frodo Baggins, Samwise Gamgee, Meriadoc Brandybuck and Peregrin Took. The main story is followed in the book by six appendices that provide a wealth of historical and linguistic background material.

Taking over 12 years to write, edit and re-write, The Lord of the Rings was long regarded as 'mere fantasy', but has come to be seen as an extraordinarily well crafted work of literature. Tolkien's skill as an philologist, writer and dramatist, as well as his contacts with other writers (see Inklings'), produced a novel where every sentence, paragraph and chapter is not only grammatically perfect, but often dramatically impactful.

Along with Tolkien's other writings, The Lord of the Rings has been subjected to extensive analysis of its literary themes and origins. Although a major work in itself, the story is only the last movement of a mythology that Tolkien had worked on since 1917. Influences on this earlier work, and on the story of The Lord of the Rings, include philology, mythology, industrialization, and religion, as well as earlier fantasy works and Tolkien's experiences in World War I. The Lord of the Rings in its turn is considered to have had a great effect on modern fantasy, and the impact of Tolkien's works is such that the use of the words "Tolkienian" and "Tolkienesque" have been recorded in the Oxford English Dictionary.

The great and enduring popularity of The Lord of the Rings has led to numerous references in popular culture, the founding of many societies by fans of Tolkien's works, and the publication of many books about Tolkien and his works. The Lord of the Rings has inspired, and continues to inspire, artwork, music, films and television, video games, and subsequent literature. Adaptations of The Lord of the Rings have been made for radio, theatre, and film. The 2001-2003 release of the widely acclaimed Lord of the Rings film trilogy prompted a new surge of interest in The Lord of the Rings and Tolkien's other works.