A happy ending is an ending of the plot of a work of fiction in which almost everything turns out for the best for the hero or heroine, their sidekicks, and almost everyone except the villains.

In storylines where the protagonists are in physical danger, a happy ending would mainly consist in their surviving and successfully concluding their quest or mission; where there is no physical danger, a happy ending is often defined as lovers consummating their love despite various factors which may have thwarted it; and a considerable number of storylines combine both factors.

A Times review of The Spy Who Came in from the Cold strongly criticised John le Carré for failing to provide a happy ending, and gave unequivocal reasons why in the reviewer's opinion (shared by many others) such an ending is needed: "The hero must triumph over his enemies, as surely as Jack must kill the giant in the nursery tale. If the giant kills Jack, we have missed the whole point of the story."

A happy ending is epitomized in the standard fairy tale ending phrase, "happily ever after" or "and they lived happily ever after." (The Arabian Nights have the more restrained formula they lived happily until there came to them the One who Destroys all Happiness (i.e. Death). Satisfactory happy endings are happy for the reader as well, in that the characters he or she sympathizes with are rewarded.

The presence of a happy ending is one of the key points that distinguishes melodrama from tragedy. In certain periods, the endings of traditional tragedies such as Macbeth or Oedipus Rex, in which most of the major characters end up dead, disfigured, or discountenanced, have been actively disliked. In the eighteenth century, the Irish author Nahum Tate sought to improve Shakespeare's King Lear in his own heavily modified version in which Lear survives and Cordelia marries Edgar. Most subsequent critics have not found Tate's amendments an improvement. Happy endings have also been fastened to Romeo and Juliet and Othello. Not everybody agrees on what a happy ending is.

An interpretation of The Merchant of Venice's forced conversion of Shylock to Christianity is that it was intended as a happy ending - since Shakespeare's audience took for granted that being a Christian is a happier and more satisfactory situation than not being one. However, as a Christian, he could no longer impose interests, undoing his schemes in the play.

Similarly, based on the assumptions about women's role in society prevalent at the time of writing, The Taming of the Shrew's concluding with the complete breaking of Kate's rebelliousness and her transformation into an obedient wife counted as a happy ending.

A happy ending only requires that the main characters be all right. Millions of innocent background characters can die, but as long as the characters that the reader/viewer/audience cares about survive, it is still a happy ending. Roger Ebert comments ironically in his review of Roland Emmerich's The Day After Tomorrow; "Billions of people may have died, but at least the major characters have survived. Los Angeles is leveled by multiple tornadoes, New York is buried under ice and snow, the United Kingdom is flash-frozen, and lots of the Northern Hemisphere is wiped out for good measure. Thank god that Jack, Sam, Laura, Jason and Dr. Lucy Hall survive, along with Dr. Hall's little cancer patient."