Measure for Measure is a play by William Shakespeare that tells the story of Vienna under the temporary rule of Angelo, Lord Deputy to the Duke, Vincentio. Originally classified as a comedy it is now considered as one of Shakespeare's problem plays.

1. Vincentio: the Duke.
2. Angelo: Lord Deputy in the Duke's absence.
3. Escalus: an Ancient Lord.
4. Claudio: a young Gentleman.
5. Isabella: sister to Claudio.
6. Mariana: betrothed to Angelo.
7. Juliet: beloved of Claudio.
8. Lucio: a flamboyant bachelor and friend of Claudio.
9. Mistress Overdone: A bawd, runs a brothel.

Vincentio, the Duke of Vienna, takes leave on a diplomatic mission and entrusts his rule to his deputy Angelo. In secret, Vincentio has planned to disguise himself as a friar in order to observe his city's affairs - and especially the actions of Angelo. Under Vincentio, the city's harsh laws against fornication have been laxly enforced and Vincentio intends to let Angelo, who is a known hard-liner, enforce them uncompromisingly. The plan works well and Claudio, a young nobleman who has impregnated his fiance Juliet, is sentenced to death by Angelo. Claudio's sister, the postulate nun Isabella intervenes on his behalf, and is offered a deal: Angelo will spare Claudio's life if Isabella will sleep with Angelo. Isabella refuses and also realizes that she will be unsuccessful if she makes a public accusation against Angelo. The disguised Vincentio finally intervenes and helps plan two tricks to thwart Angelo. Eventually Vincentio "returns" to Vienna and holds court on a petition against Angelo. The play ends with Vincentio revealing that he was in fact disguised as the friar and making right all the problems created by Angelo's rule.

Despite its classic comedy setting and ending, Measure for Measure's themes of sex, morality, and the law are darker than many of Shakespeare's other comedies. The term "Problem Play" was coined by critic F. S. Boas to describe plays in which the resolution of the themes and debates seems inadequate and, in the final act, the deliverance of justice and completion one expects does not occur. Other definitions have been proposed since, however all center around the issue that these plays cannot be easily assigned to the traditional categories of comedy or tragedy.

• "Some rise by sin, and some by virtue fall."

• "Truth is truth to the end of reckoning."

• "Virtue is bold, and goodness never fearful."

• "The miserable have no other medicine, but only hope."

• "O, what may man within him hide, though angel on the outward side!"