Night letter)[1] is a song by South Korean singer-songwriter IU for her fourth studio album Palette (2017).

Marking her return to music, the stripped-down song offers a sharp departure from her previous single "Twenty-Three".

"Through the Night" was a major success in South Korea, debuting at number two on the Gaon Digital Chart before becoming IU's 14th number one single in South Korea the following week—enabling her to extend her lead over idol groups Big Bang, 2NE1 and Sistar, which each had nine.

IU's vocals are described as being warm, and yet apprehensive in this love song which delves into the acoustic and folk genres.

South Korean music portal IZM, included the song on their list of "10 singles that represented 2017" explaining "There was no other song this year that expressed more precisely the precious, small, and pure emotion that wells up when penning a letter for someone you love all night as this one."

[9] The song shot to the top of the Instiz iChart upon release, and eventually achieved a Perfect All-Kill, as the single hit Number 1 on all of the major South Korean music sites simultaneously.

The track also debuted at number one on both Gaon's Mobile and Background Music charts, solidifying the song's omnipresence in the industry.

[19] The video begins with a scene depicting a traditional countryside home, with birds chirping audibly in the background.

It was chosen in an effort to incorporate books with vertical writing to add to the old-fashioned theme of the music video.

"Through the Night"'s only performance on a music show was on April 23's episode of Inkigayo, where the song had won the previous week.

[22] She also performed the song on 32nd Golden Disc Awards alongside her other hits, "Can't Love You Anymore" and "Autumn Morning".