Don Quixote, the full title being The Ingenious Gentleman Don Quixote of La Mancha, is a Spanish novel by Miguel de Cervantes. Originally published in two parts in 1605 and 1615, the novel is considered a founding work of Western literature and the first modern novel. The novel has been labelled by many well-known authors as the "best novel of all time" and the "best and most central work in world literature". Don Quixote is also one of the most-translated books in the world and one of the best-selling novels of all time.

The plot revolves around the adventures of a member of the lowest nobility, a hidalgo from La Mancha named Alonso Quijano, who reads so many chivalric romances that he loses his mind and decides to become a knight-errant (caballero andante) to revive chivalry and serve his nation, under the name Don Quixote de la Mancha. He recruits as his squire a simple farm labourer, Sancho Panza, who brings an earthy wit to Don Quixote's lofty rhetoric. In the first part of the book, Don Quixote does not see the world for what it is and prefers to imagine that he is living out a knightly story meant for the annals of all time. However, as Salvador de Madariaga pointed out in his Guía del lector del Quijote (1972 [1926]), referring to "the Sanchification of Don Quixote and the Quixotization of Sancho", as "Sancho's spirit ascends from reality to illusion, Don Quixote's declines from illusion to reality".

The book had a major influence on the literary community, as evidenced by direct references in Alexandre Dumas's The Three Musketeers (1844), and Edmond Rostand's Cyrano de Bergerac (1897) as well as the word quixotic. Mark Twain referred to the book as having "swept the world's admiration for the mediaeval chivalry-silliness out of existence". It has been described by some as the greatest work ever written.

For Cervantes and the readers of his day, Don Quixote was a one-volume book published in 1605, divided internally into four parts, not the first part of a two-part set. The mention in the 1605 book of further adventures yet to be told was totally conventional, did not indicate any authorial plans for a continuation, and was not taken seriously by the book's first readers.

Cervantes, in a metafictional narrative, writes that the first few chapters were taken from "the archives of La Mancha", and the rest were translated from an Arabic text by the Moorish historian Cide Hamete Benengeli.

Alonso Quixano is an hidalgo nearing 50 years of age who lives in a deliberately unspecified region of La Mancha with his niece and housekeeper. While he lives a frugal life, he is full of fantasies about chivalry stemming from his obsession with chivalric romance books. Eventually, his obsession becomes madness when he decides to become a knight errant, donning an old suit of armor. He renames himself "Don Quixote", names his old workhorse "Rocinante", and designates Aldonza Lorenzo (a slaughterhouse worker with a famed hand for salting pork) his lady love, renaming her Dulcinea del Toboso.

As he travels in search of adventure, he arrives at an inn that he believes to be a castle, calls the prostitutes he meets there "ladies", and demands that the innkeeper, whom he takes to be the lord of the castle, dub him a knight. The innkeeper agrees. Quixote starts the night holding vigil at the inn's horse trough, which Quixote imagines to be a chapel. He then becomes involved in a fight with muleteers who try to remove his armor from the horse trough to water their mules. In a pretend ceremony, the innkeeper dubs him a knight to be rid of him and sends him on his way.

Quixote next encounters a servant named Andres who is tied to a tree and being beaten by his master over disputed wages. Quixote orders the master to stop the beating, untie Andres and swear to treat his servant fairly. However, the beating is resumed, and redoubled, as soon as Quixote leaves.