All's Well That Ends Well is a play by William Shakespeare, published in the First Folio in 1623, where it is listed among the comedies. There is a debate about the date of its composition, with possible dates ranging from 1598 to 1608.

The play is considered one of Shakespeare's "problem plays", those that pose ethical dilemmas that require more than typically simple solutions.

Helena, the low-born ward of a French-Spanish countess and daughter of a recently deceased physician, is in love with the countess's son, Bertram, who is indifferent to her. Bertram goes to Paris to replace his late father as attendant to the ailing King of France. Helena follows Bertram, ostensibly to offer the King her services as a healer. The King is sceptical, and she guarantees the cure with her life: if he dies, she will be put to death, but if he lives, she may choose a husband from the court.

The King is cured and Helena chooses Bertram, who rejects her, owing to her poverty and low status. The King forces him to marry her, but after the ceremony Bertram immediately goes to war in Italy without so much as a goodbye kiss. He says he will marry her only after she has carried his child and got his family ring from him. Helena returns home to the countess, who is horrified at what her son has done, and claims Helena as her child in Bertram's place.

In Italy, Bertram is a successful warrior and becomes infatuated with Diana, the virgin daughter of an impoverished local noblewoman. Helena follows Bertram to Italy, befriends Diana, and arranges to take Diana's place in bed with him. Diana obtains Bertram's ring in exchange for one of Helena's. In this way Helena, without Bertram's knowledge, consummates their marriage and is given his ring.

Helena fakes her own death. Bertram, thinking he is free of her, comes home. He tries to marry a French lord's daughter with whom he had previously fallen in love, but Diana turns up and causes the engagement to be broken off. Helena appears and explains the ring swap, announcing that she has fulfilled Bertram's challenge; Bertram, impressed by all she has done to win him, swears his love to her. Thus all ends well.

There is a subplot about Parolles, a disloyal friend of Bertram's. Helena, Lafew, the Countess, her fool Lavatch and the two Lords Dumaine have all realised that Parolles is a boastful coward, but Bertram still takes him to war with him. The two Lords convince Parolles to cross into enemy territory to fetch a drum lost in battle. While he is on his way, they pose as enemy soldiers, kidnap him, blindfold him, and, with Bertram observing, get him both to betray his friends and to surrender a letter warning Diana about Bertram's lascivious character.

The play is based on the tale of Giletta di Narbona (tale nine of day three) of Boccaccio's The Decameron. F. E. Halliday speculated that Shakespeare may have read a French translation of the tale in William Painter's Palace of Pleasure.