A room at the Garter Inn
Falstaff and his servants, Bardolfo and Pistola, are drinking at the inn. Dr Caius bursts in and accuses Falstaff of burgling his house and Bardolfo of picking his pocket. He is ejected. Falstaff hands a letter to each of his servants for delivery to Alice Ford and Meg Page, two wealthy married women. In these two identical letters, Falstaff professes his love for each of the women, although it is access to their husbands' money that he chiefly covets. Bardolfo and Pistola refuse, claiming that honour prevents them from obeying him. Falstaff dispatches his page, Robin, to deliver the letters. Falstaff delivers a tirade at his rebellious followers (L'onore! Ladri...! / "Honour! You rogues...!") telling them that honour is a mere word and is of no practical value. He chases them out of his sight.
Alice and Meg have received Falstaff's letters. They compare them, see that they are identical and, together with Mistress Quickly and Nannetta Ford, resolve to punish Falstaff. Meanwhile, Ford has been warned of the letters by Bardolfo and Pistola. All three are thirsty for revenge, and are supported by Dr Caius and Fenton, a young gentleman. To Ford's disapproval, Fenton is in love with Nannetta. Finding a moment to be alone, the young lovers exchange banter. They are interrupted by the return of Alice, Meg and Mistress Quickly. The act ends with an ensemble in which the women on one side of the stage and the men on the other plan revenge on Falstaff.
A room at the Garter Inn
Falstaff is alone at the inn. Bardolfo and Pistola, now in the pay of Ford, enter and pretend to beg for forgiveness for past transgressions. They announce to their master the arrival of Mistress Quickly, who delivers an invitation to go to Alice's house that afternoon between the hours of two and three. She also delivers an answer from Meg 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, masquerading as "Signor Fontana", supposedly an admirer of Alice; he offers money to the fat knight to seduce her. Falstaff is puzzled at the request, and "Fontana" explains that if Alice succumbs to Falstaff, it will then be easier for Fontana to overcome her virtuous scruples. Falstaff agrees with pleasure and reveals that he already has a rendezvous arranged with Alice for two o'clock – the hour when Ford is always absent from home. Falstaff goes off to change into his best clothes; Ford is consumed with jealousy (È sogno o realtà? / "Is it a dream or reality?"). When Falstaff returns in his finery, they leave together with elaborate displays of mutual courtesy.
A room in Ford's house
The three women plot their strategy ("Gaie Comari di Windsor" / "Merry wives of Windsor, the time has come!"). They are in high spirits, but Alice notices that Nannetta is not. This is because Ford plans to marry her to Dr Caius, a man old enough to be her grandfather; the women reassure her that they will prevent it. Mistress Quickly announces Falstaff's arrival and 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 impending arrival of Ford with a retinue of henchmen to catch his wife's lover. Falstaff hides first behind the screen and then the women hide him in the hamper. In the meantime Fenton and Nannetta have hidden behind the screen. The men hear the sound of a kiss behind it. They assume it is Falstaff with Alice, but instead they find the young lovers. Ford orders Fenton to leave. Inside the hamper Falstaff is almost suffocating. While the men resume the search of the house Alice orders her servants to throw the hamper through the window into the River Thames, where Falstaff is compelled to endure the jeers of the crowd.
Before the inn
Falstaff glumly curses the sorry state of the world. Some mulled wine soon improves his mood. Mistress Quickly enters and delivers another invitation to meet Alice. Falstaff at first wants nothing to do with it, but she persuades him. He is to meet Alice at midnight at Herne's Oak in Windsor Great Park dressed up as the Herne the Hunter. He and Mistress Quickly go inside the inn. Ford has realised his error in suspecting his wife, and together they and their allies have been watching secretly, and now concoct a plan for Falstaff's punishment. Dressed as supernatural creatures, they will ambush and torment him at midnight. Ford privately proposes a separate plot to Caius: Nannetta will be disguised as Queen of the Fairies, Caius will wear a monk's costume, and Ford will join the two of them with a nuptial blessing. Mistress Quickly overhears, and quietly vows to thwart Ford's scheme.
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's and Caius's plans. Nannetta, as 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 Alice is interrupted by the announcement that witches are approaching, and the men, disguised as elves and fairies, soundly thrash Falstaff. At length he recognises Bardolfo in disguise. The joke is over, and Falstaff acknowledges that he has received his due. Ford announces that a wedding shall ensue. Caius and the Queen of the Fairies enter. A second couple, also in masquerade, ask Ford to deliver the same blessing for them as well. Ford conducts the double ceremony. Caius finds that instead of Nannetta, his bride is the disguised Bardolfo, and Ford has unwittingly blessed the marriage of Fenton and Nannetta. Ford accepts the fait accompli with good grace. 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! / "Everything in the world is a jest...").