Season one covers the length of Tom Perrotta's novel 'The Leftovers', the second and third seasons are completely original material.

On October 14, 2014, over a month after season one concluded, HBO aired the entire season all day as a nod to the date in which the "great departure" occurred in the show.

The character of Kevin Garvey in The Leftovers novel (portrayed by Justin Theroux in the show) is the mayor of Mapelton, New York, not the Chief of Police as he is in the show.

Justin Theroux's wife Jennifer Aniston refused to help her husband with rehearsing lines, because she wanted to avoid spoilers. Aniston is a huge fan of the series.

In The Leftovers novel, the character of Jill Garvey (portrayed by Margaret Qualley in the show) has a shaved head.

No character appears in every episode.

According to Amy Brenneman, the screenplays didn't have a lot of information of her character, just descriptions of the kind of looks and gestures Laurie would do on the scene. So Brenneman would call co-creator Damon Lindelof and asked for information so she knew better what Laurie was going through.

The ceiling of Virgil's trailer is covered with light bulbs. This is a reference to Ralph Ellison's classic of American literature, Invisible Man, in which the protagonist is an outlaw squatter in a basement that he has outfitted with 1,369 light bulbs.

After filming the sixth episode, production shut down for two weeks. According to HBO this was done to give the creative team more time to prepare the last episodes, because rumor has it that it was so co-creator Damon Lindelof would make changes, because the network wasn't happy with aspects of the show so far.

Liv Tyler admitted on an interview given in May 2017 that Meg was such a contradictory and mysterious character that after a while she started to play her without trying to understand her actions and just performed the scenes as written.

On December 11, 2015, HBO confirmed via their official twitter account the show is renewed for the 3rd and final season.

Christopher Eccleston plays Matt Jamison, a priest whose story lines heavily revolve around his faith. In real life, Eccleston is an Atheist.

Regina King shot season 2 simultaneously with the second season of American Crime (2015).

Christopher Eccleston plays a priest devoted to disproving the rapture here. In The Second Coming (2003), he plays a man claiming to be the son of God who threatens to bring about the rapture.

Nora has the final line of dialogue in each season finale. Season 1 "Look what I found.", Season 2 "You're home.", and Season 3 "I'm here."

For season 2, each episode title is either a word/phrase that a character says to another or is an object that has a central focus of the plot. The only exception is the episode titled No Room at the Inn, which is an obvious reference to the fact that Mary is pregnant and she and Matt cannot return or get access to the inside of Jarden.