A comedy in five acts, one of the later plays, first performed in 1609-10 and published in the First Folio of 1623, from an authorial copy imperfectly prepared as a promptbook. Set in the pre-Christian Roman world, Cymbeline draws its main theme, that of a wager by a husband on his wife's fidelity, from Giovanni Boccaccio's Decameron.

Imogen, the daughter of the British king Cymbeline, goes against her father's wishes and secretly marries a lowborn gentleman, Posthumus, instead of his oafish stepson, Cloten. Cloten is the son of Cymbeline's second wife, a villainous woman who has made the king her puppet. Cymbeline banishes Posthumus, exiling him to Italy. Before his departure, Posthumus gives Imogen a bracelet, and he in return gives her a ring. Whilst in Italy, Posthumus encounters a smooth-tongued Italian named Iachimo. Iachimo argues that all women are naturally unchaste; to prove his point he makes a wager with Posthumus that he will be able to seduce Imogen. He goes to the British court and, failing in his initial attempt to convince the princess to sleep with him, resorts to trickery. Hiding in a large chest, which he has it sent to her room; later in the night he slips out, and steals her bracelet whilst she sleeps, He also, examining Imogen as she sleeps, makes note of a mole not easily seen.

Cloten, meanwhile, continues to pursue Imogen, but she repeatedly rebuffs him harshly. He becomes furious and vows revenge, meanwhile, she worries over the loss of her bracelet. In the meantime, Iachimo has returned to Italy, and, displaying the stolen bracelet and an intimate knowledge of the details of Imogen's bedchamber, convinces Posthumus that he won the bet. Whereupon Posthumus gives up the ring, that Imogen gave him.

As these events are occurring, the malicious stepmother has arranged for her physician to create a poison for Pisanio, a servant and friend of Posthumus. The physician, distrustful of the wicked queen, prepares instead a type of sleeping potion. This is given to Pisanio.

as a page. Going in search for her husband, He also gives the potion, which he believes is a "sovereign restorative," to Imogen, though he reports to Posthumus, that he has killed her.

Cymbeline angers Lucius, a Roman ambassador to the point that Rome declares war on Britain over an unpaid tribute to Caesar. Imogen, still disguised as the page Fidele, however, soon becomes lost in the wilds of Wales, and she comes upon a cave where Belarius, an unjustly banished nobleman, lives with his two sons, Guiderius and Arviragus. In fact, the two young men are not his sons but Cymbeline's; Belarius has kidnapped them to avenge his banishment, though they themselves are ignorant of their true parentage. They welcome Imogen, who is still dressed as a boy. At this time, Cloten appears disguised in Posthumus's clothes; he is on the hunt for Imogen and Posthumus (who he believes to be in Milford Haven). having come in pursuit of Imogen; he fights a duel with Guiderius, who kills him after being insulted. He then cuts off Cloten's head and tosses it into the river.

Imogen, feeling ill, drinks a potion the queen has given her, under the impression, it was medicinal, and the queen herself believed it to be a poison, unbeknownst to either, however, the draught merely induces a deep sleep that resembles death. Belarius and his adoptive sons come upon Imogen and, heart-broken, lay her body beside that of the slain Cloten. Awaking after they have left the scene, she mistakes the body of Cloten for that of Posthumus, and she sinks into despair. and promptly faints. When she recovers, the despairing Imogen (still disguised as Fidele) accepts service as a page with Lucius (who happens by as she comes to).

A Roman army has invaded Britain, seeking the restoration of a certain tribute Britain has ceased to pay. The disguised Imogen hires herself out to them as a page at the court of Cymbeline; the Queen has begun to go mad from the disappearance of Cloten.

Posthumus and Iachimo are traveling with the Roman army, but Posthumus switches to the garb of a British peasant and fights valiantly for Britain. Indeed, in his combat he actively seeks death: since he believes his servant to have carried out his orders and killed Imogen, actions he regrets asking his servant to undertake. The Romans are defeated, thanks to the intervention of Belarius, Guiderius, and Arviragus, and Posthumus. Posthumus, still trying to punish himself, switches back to Roman garb and allows the British to take him prisoner.

That night, the god Jupiter promises the spirits of Posthumus's dead ancestors that he will care for their descendant, and grants Posthumus a strange prophetic vision. The next day, Cymbeline calls the prisoners before him, and the confusions are sorted out. Posthumus and Imogen are reunited, and they forgive a contrite Iachimo, Lucius, and Imogen (Fidele) who were also captured and brought to Cymbeline. The Queen, her condition worsening, confesses her evil doings on her deathbed before expiring, leaving the king free of her evil influence. In the ensuing confessions that follow, Iachimo confesses to stealing the bracelet and lying, Posthumus reveals his own identity, Pisanio admits his part in helping Imogen escape, Belarius admits to kidnapping the two boys, and Posthumus and Imogen are reunited and allowed to stay married. A soothsayer interprets Posthumus's vision as the rejoining of Cymbeline's family (which has happened). Finally, Cymbeline releases his prisoners and comes to peaceful terms with Rome. As a final gesture, Cymbeline frees the Roman prisoners and even agrees to resume paying the tribute.

Shakespeare shows great dramatic skill in weaving together many different elements of plot, period, and place. The open-air scenes in Wales, Iachimo's concealment in a trunk in Imogen's bedchamber, the supposed deaths of Posthumus and of the disguised Imogen, the battle between the Britons and Romans, the vision of the eagle-borne Jupiter--all these are in preparation for the amazing complications of the final scene of the play, where (it has been calculated) there are 24 distinct "revelations" in the space of 455 lines. (For the song "Hark, hark! the lark," see Audiovisual Features.)