''One Day'' follows the story of Dexter Mayhew and Emma Morley, who meet and form a friendship as they graduate from university in 1988 and charts the progress of their lives by 'checking in' on their lives annually on the anniversary of the day they met.
A novel by David Nicholls and adapted into a [[TheFilmOfTheBook film]] in 2011 starring Creator/AnneHathaway and Jim Sturgess.
!!This novel provides examples of:
* AmicablyDivorced: [[spoiler: Dex]] and Sylvie.
* BetterAsFriends: What Dex and Emma initially settle on.
* BettyAndVeronica: Emma is the Betty to all of Dex's other love interests as Veronicas, while he is the Veronica to her Bettys (Ian especially).
* BookEnds: The first day Emma and Dex spent together.
* BrainyBrunette: Emma.
* TheCasanova: Dex, especially in his early years.
* DisposableFiance: Ian. Their relationship is shown to be one more of convenience than passion.
* LadykillerInLove: Eventually.
* MoodWhiplash: From heartwarming to tearjerker in the space of [[spoiler: one traffic accident]].
* RomanticFalseLead: Several. Ian and Sylvie are the most prominent.
* RomanticRunnerUp: Ian again.
* ShotgunWedding: Implied between [[spoiler: Dex]] and Sylvie once she got pregnant.
* StarCrossedLovers: Sort of. Their timing is off, and often when one is single the other is not, but also they both need to go through a significant amount of CharacterDevelopment before being mature enough to handle their own relationship.
* UptownGirl: Inverted. Dex comes from a wealthy, upper-class family and Emma from a more modest background.
* WhatTheHellHero: Emma calls out Dex on his shallow, party-boy lifestyle. As does his mother.
* YourCheatingHeart: [[spoiler: Sylvie cheats on Dex with his boss]].
** [[spoiler: Emma also has an affair with the married headmaster of the school where she teaches.]]