Act 1

A room at the Garter Inn
Falstaff is surrounded by his servants Bardolfo, Pistola, and the innkeeper. Dr. Caius arrives and accuses him of robbery, but the excited doctor is soon ejected. Falstaff hands two letters to each of his servants for delivery to Mistress Alice Ford and to Mistress Meg Page, two wealthy married women. In these two identical letters, Falstaff professes his love for each of them, although it is really their husbands’ money that he covets. His servants Bardolfo and Pistola refuse, claiming that ‘honour’ prevents them from obeying him. Falstaff sends the letters by a page instead. Falstaff then rebuffs his "honourable" servants by saying that honour is intangible and cannot be either eaten or felt such as hair being pulled or being saved from death by honour (L'onore! Ladri...! / “Honour! You rogues...!”) and chases them out of his sight.

Ford's garden
Alice and Meg have received Falstaff's identical letters. They are furious about the letters and in conjunction with Mistress Quickly and Nannetta Ford, resolve to punish the knight. Meanwhile, Ford has been warned of the letters by Bardolfo and Pistola. All three are thirsty for revenge. Alice walks out of the scene since Ford is very jealous and does not want him to find out. Finding a moment to be alone for once with Nannetta, Fenton (an employee of Ford) woos the boss' daughter, who responds favorably. The women return home and Mistress Quickly is requested to invite Falstaff to a rendez-vous with Alice. The men also arrive at the scene, and Bardolfo and Pistola are persuaded to introduce Ford to Falstaff, but under an assumed name. At the end all swear revenge on Lord Falstaff.

Act 2

A room at the Garter Inn
Bardolfo and Pistola (now in the pay of Ford), pretending to beg for forgiveness for past transgressions, announce to their master the arrival of Mistress Quickly, who delivers the invitation to go to Alice's house that very day between the hours of two and three. She also delivers an answer by Mistress Page and assures Falstaff that neither is aware of the other's invitation. Falstaff celebrates his potential success ("Va, vecchio John" / "Go, old Jack, go your own way”). Ford is now introduced as Signor Fontana; he offers money to the fat knight to intercede for him with Mistress Ford. Falstaff is puzzled at the request, "Fontana" says that if Mistress Ford falls for Falstaff, it will be easier that she will fall for Fontana too. Falstaff agrees with pleasure and reveals that he has already succeeded, because he has a rendez-vous with her at two – the hour when he is always absent from home; while Falstaff dresses in his most splendid array, Ford is consumed with jealousy (È sogno o realtà? / "Is it a dream or reality?").

A room in Ford's house
The three women plot their strategy ("Gaie Comari di Windsor" / “Merry wives of Windsor, the time has come!"). Nannetta also learns that her father plans to marry her with Dr. Caius, a man old enough to be her great-grandfather, but all the women declare that that will not happen. Mistress Quickly announces Falstaff's arrival, Mistress Ford has a large hamper and a screen placed in readiness. Falstaff's attempts to seduce Alice with tales of his past glory ("Quand'ero paggio del Duca di Norfolk" / “When I was page to the Duke of Norfolk I was slender”) are cut short, as Mistress Quickly reports the arrival of Master Ford who comes with a huge retinue of henchmen to lynch his wife's lover. When the angry Ford and his friends appear with the aim of catching Falstaff red handed; he hides first behind the screen and then the ladies hide the knight in the hamper. In the meantime, Fenton and Nannetta have hidden behind the screen. Upon returning from their search for Falstaff, the men hear the sound of a kiss behind the screen. They think that they will at last grab Falstaff with Alice, but instead find Fenton, who is ordered by Ford to leave. In the meantime Falstaff has been complaining that he is sweating too much inside the hamper. When the men again proceed with the search, the women order the hamper to be thrown into the river through the window, where Falstaff is compelled to endure the jeers of the crowd.

Act 3

Before the Garter inn
In a gloomy mood, Falstaff curses the sorry state of the world. However, some mulled wine soon improves his mood. The fat knight receives another invitation through Mistress Quickly, who blames the servants for what happened to him, the invitation consists of going to Herne's Oak dressed up as the Herne the Hunter, aka the Black Huntsman. Although dubious at first, Falstaff promises to go. He enters the house with Mistress Quickly to be filled in with more details for his attire, and the men and women concoct a plan for his punishment. Dr. Caius is promised Nannetta's hand in marriage and is told how he may recognize her in her disguise, but the plot is overheard by Mistress Quickly.

Herne's Oak in Windsor Park on a moonlit midnight
Fenton arrives at the oak tree and sings of his happiness ("Dal labbro il canto estasiato vola" / “From my lips, a song of ecstasy flies”) ending with “Lips that are kissed lose none of their allure.” Nannetta enters to finish the line with “Indeed, they renew it, like the moon.” The women arrive and disguise Fenton as a monk, telling him that they have arranged things so as to spoil Ford and Dr. Caius' plans. Nannetta, playing the role of the Fairy Queen, instructs her helpers ("Sul fil d'un soffio etesio" / “On the breath of a fragrant breeze, fly, nimble spirits”) before all the characters arrive on the scene. Falstaff's attempted love scene with Mistress Ford is interrupted by the announcement that witches are approaching, and the men, disguised as elves and fairies, soundly thrash Falstaff, who recognizes Bardolfo in disguise and the joke is over, acknowledging that he has received his due. Ford announces that a wedding shall ensue (a second couple "coincidentally" asks to be married at that time also) and Dr. Caius finds that instead of Nannetta, he has landed Bardolfo who is dressed in the same fairy queen outfit as Nannetta and Ford unwittingly has married Fenton and Nannetta. Falstaff, pleased to find himself not the only dupe, proclaims in a fugue, which the entire company sings, that all the world is folly and all are figures of fun (Tutto nel mondo è burla... Tutti gabbati! / “All the world’s a stage”).