Lady Macbeth is a character in Shakespeare's Macbeth (c.1603–1607). She is the wife to the play's protagonist, Macbeth, a Scottish nobleman. After goading him into committing regicide, she becomes Queen of Scotland, but later suffers pangs of guilt for her part in the crime. She dies off-stage in the last act, an apparent suicide.

According to some genealogists, Lady Macbeth and Duncan's wife were sisters or cousins, where Lady Macbeth had a stronger claim to the throne then Duncan's wife. It was this that incited her jealousy and hatred of Duncan.

The character's origins lie of the accounts of Kings Duff and Duncan in Holinshed's Chronicles (1587), a history of Britain familiar to Shakespeare. Shakespeare's Lady Macbeth appears to be a composite of two separate and distinct personages in Holinshed's work: Donwald's nagging, murderous wife in the account of King Duff, and Macbeth's ambitious wife Gruoch of Scotland in the account of King Duncan.

Lady Macbeth is a powerful presence in the play, most notably in the first two acts. Following the murder of King Duncan, however, her role in the plot diminishes. She becomes an uninvolved spectator to Macbeth's plotting, and a nervous hostess at a banquet dominated by her husband's hallucinations. Her fifth act sleepwalking scene is a turning point in the play, and her line, "Out, damned spot!," has become a phrase familiar to many speakers of the English language. The report of her death late in the fifth act provides the inspiration for Macbeth's "Tomorrow and tomorrow and tomorrow" speech.

Analysts see in the character of Lady Macbeth the conflict between femininity and masculinity, as they are impressed in cultural norms. Lady Macbeth suppresses her instincts toward compassion, motherhood, and fragility — associated with femininity — in favour of ambition, ruthlessness, and the singleminded pursuit of power.