Bilbo's Last Song (at the Grey Havens) is a poem by J. R. R. Tolkien, written as a pendant to his fantasy The Lord of the Rings. It was first published in a Dutch translation in 1973, subsequently appearing in English on posters in 1974 and as a picture-book in 1990. It was illustrated by Pauline Baynes, and set to music by Donald Swann and Stephen Oliver. The poem's copyright was owned by Tolkien's secretary, to whom he gave it in gratitude for her work for him.

In 1968, aged seventy-six, Tolkien decided to retire from his house at 76 Sandfield Road, Headington, Oxford to a bungalow at 19 Lakeside Road, Poole, near Bournemouth. On 17 June, while preparing for his relocation, he fell downstairs and badly injured his leg. He needed surgery, a plaster cast, crutches and several weeks of recuperation in the Nuffield Orthopaedic Centre and Bournemouth's Miramar Hotel before he was well enough to resume living independently. When he finally moved into his new home on 16 August, he found that unpacking his forty-eight crates of books and papers was too much for him. He sought the help of Margaret Joy Hill, a secretary whom his publisher, Allen & Unwin, had assigned to deal with his fan mail, and whom he and his wife had come to regard almost as a second daughter. During circa 14–18 October, while Hill was helping Tolkien to set up his new office and library, she made a discovery. "As I picked up a pile of books in my arms and put them on the shelf", she recalled in 1990, "something dropped out from between two of them. It was an exercise book: just the cover with a single sheet between, and on the page, a poem. [Tolkien] asked what it was; I gave it to him, and he read it aloud. It was Bilbo's Last Song.

The fan mail that Hill brought from Allen & Unwin to Tolkien included many packages. Hill and Tolkien used to enjoy guessing what kind of presents his devotees had sent to him. "One day", she remembered, "as he cut the string on a packet, he said 'If I find this is a gold bracelet studded with diamonds, it is to be yours.' Of course it wasn't, but the bracelet became a joke between us." On a later visit on circa 3 September 1970, Hill recollected, "[Tolkien] said: 'We've opened all the parcels and there was no gold bracelet for you. I've decided that Bilbo's Last Song is going to be your bracelet.'" Tolkien formalized his gift on 28 October 1971, sending Hill an annotated typescript of the poem and a covering letter: "Dear Joy, I have appended the following note to the copy of Bilbo's Last Song (at the Grey Havens) which I retain. A copy of this poem was presented to Miss M. Joy Hill on 3 September 1970, and also the ownership of the copyright of this poem, with the intention that she should have the right to publish it, or to dispose of the copyright, as she might wish to do, at any time after my death. This was a free gift as a token of gratitude for her work on my behalf. J. R. R. Tolkien."

Tolkien died on 2 September 1973, and Hill arranged for the poem to be published shortly afterwards. When she herself died in 1991, the poem's copyright was bequeathed to the Order of the Holy Paraclete, an Anglican educational foundation.

The poem comprises three stanzas, each containing four rhyming couplets. It is a dramatic lyric that the hobbit Bilbo Baggins is supposed to have composed as he contemplated his approaching death – a nunc dimittis that could have been, but was not, incorporated into the final chapter of The Lord of the Rings. The context of Bilbo's making of the poem is that he, the hobbits Frodo and Sam and the elves Elrond and Galadriel have travelled to Mithlond, the Grey Havens, where they have been met by the elvish shipwright Círdan and the wizard Gandalf. Bilbo, Frodo, Elrond, Galadriel and Gandalf are preparing to board the elven ship that will carry them magically away from the mortal world of Middle-earth to the Undying Lands beyond the sunset. Bilbo's verses acknowledge the ending of his day and the dimming of his eyes, bid farewell to the friends whom he will leave behind and look forward to the Lonely Star's guiding him to "west of West", "where night is quiet and sleep is rest".

Little is known about the poem's development. According to Christina Scull and Wayne G. Hammond, it began as early as the 1920s or 1930s in a composition in Old Norse titled Vestr um haf – "West over sea". As Scull and Hammond point out, the poem cannot have reached its final form until after Tolkien had conceived how The Lord of the Rings would conclude. A progress report on the writing of the book that Tolkien sent to his son Christopher on 29 November 1944 shows that the coda of his story had taken shape in his mind long before it was published in 1955: "The final scene will be the passage of Bilbo and Elrond and Galadriel through the woods of the Shire on their way to the Grey Havens. Frodo will join them and pass over the Sea."

Bilbo's voyage to the Undying Lands is reminiscent of several other journeys in English literature. Scull and Hammond observe that Bilbo's Last Song is somewhat like Tennyson's Crossing the Bar (1889), a sixteen-line religious lyric (sharing some of Tolkien's poem's vocabulary) in which a sea voyage is a metaphor for a faithful death. Other precursors of Tolkien's poem are the legend of the carrying of the wounded King Arthur to the magical isle of Avalon and the quest of Reepicheep to sail to the holy country of the divine lion Aslan in Tolkien's friend C. S. Lewis's The Voyage of the Dawn Treader.

Bilbo's Otherworld journey has further parallels in writings of Tolkien's own. The figure of the mortal who sails from the quotidian world to a paradise beyond the sea is a motif that recurs in Tolkien's poems and stories throughout his creative life. Examples are Roverandom, Eriol in The Book of Lost Tales, Tuor in Quenta Silmarillion, Ar-Pharazôn in Akallabêth, Ælfwine in The Lost Road, St Brendan in Imram, Sam and Gimli in The Lord of the Rings and the narrator of "The Sea-Bell" in The Adventures of Tom Bombadil.