Catharsis, Latin from the Greek Katharsis 'purification', is a sudden emotional breakdown or climax that constitutes overwhelming feelings of great pity, sorrow, laughter, or any extreme change in emotion that results in the renewal, restoration and revitalization for living.

Catharsis is a form of emotional cleansing first defined by the Greek philosopher Aristotle. It refers to the sensation, or literary effect, that would ideally overcome an audience upon finishing watching a tragedy. The fact that there existed those who could suffer a worse fate than them was to them a relief, and at the end of the play, they felt ekstasis (literally, astonishment), from which the modern word exstasis and ecstasy are derived. While seemingly related to schadenfreude, it is not, however, in the sense that the audience is not intentionally led to feel happy in light of others' misfortunes; in an invariant sense, their spirits are refreshed through having greater appreciation for life.

In literary aesthetics catharsis is developed by the conjuction of stereotyped characters and unique or surprising actions. Throughout a play we do not expect the nature of a character to change significantly, rather pre-existing elements are revealed in a relatively straight-forward way as the character is confronted with unique actions in time. This can be clearly seen in Oedipus Rex where King Oedipus is confronted with ever more outrageous actions until emptying generated by the death of his mother-wife and his act of self-blinding. As a literary effect, catharsis should be compared with the equivalent effects for epic and poetic forms of kairosis and kenosis.

In contemporary aesthetics catharsis may also refer to any emptying of emotion experienced by an audience in relation to drama. This exstasis can be perceived in comedy, melodrama and most other dramatic forms. Deliberate attempts, on political or aesthetic bases, to subvert the structure of catharsis in theatre have occurred. For example, Bertold Brecht viewed catharsis as a pap for the bourgeois theatre audience, and designed dramas which left significant emotions unresolved, as a way to force social action upon the audience. In Brecht's theory, the absence of a cathartic resolving action would require the audience to take political action in the real world in order to fill the emotional gap they experience. This technique can be seen as early as his agit-prop play The measures taken.