''Long Day's Journey Into Night'' is the story of a day in the life of a [[AwLookTheyReallyDoLoveEachOther loving]] but [[DysfunctionalFamily dysfunctional]] Irish-American family as it is torn apart by [[FatalFlaw addiction, resentment, and regret.]] It is also Eugene O'Neill's most autobiographical play, hence his insistence that it not be published until after his death. Winner of the 1957 Pulitzer Prize.

A well-regarded film adaptation, directed by Creator/SidneyLumet and starring Creator/KatharineHepburn as Mary, was made in 1962.

This play provides examples of:

* AuthorAvatar: O'Neill spent a great deal of his early adulthood at sea, battled with alcoholism and depression, and suffered from tuberculosis, just like Edmund.
* CreatorBreakdown
* DownerEnding: It is implied that the end scene has been and will be repeated many, many more times.
* ExtremelyShortTimespan: The play takes place between morning and midnight on a single August day in 1912.
* FatalFlaw: See above.
* GenerationXerox: Perhaps one of the morals of the play, sad as it may be.
* IgnoredEpiphany
* IncurableCoughOfDeath: [[spoiler:Actually Tuberculosis.]]
* LampshadeHanging: "What a bastard to have for a father! Christ, if you put him in a book, no one would believe it!"
* ParentsAsPeople: And how. Mary and James are depressingly human.
* TheDiseaseThatShallNotBeNamed: Literally. Edmund tries not to speak about his illness, as he believes it could be his mother's final breaking point.
* TheOphelia: Mary, especially in the last scene. Mostly due to the [[spoiler:morphine]].
** '''James''': The mad scene. Enter Ophelia!
* ShoutOutLiterature: Edmund compares himself to a [[TheSeagull seagull.]]
* ShoutOutToShakespeare: Too many to count; the Tyrones are a family of actors, after all.
* WriteWhoYouKnow: Where to begin? Everyone is directly based on his real family and even share their first named: O'Neill's father was a famous {{Melodrama}} actor named James; his addict mother's first name was Mary, although she went by Ella; and his older brother was James Jr (Jamie). There's even a fleeting reference to the dead infant son being named Eugene-- essentially O'Neill swaps names with Edmund the AuthorAvatar, the actual name for his dead sibling.