The lyrics of this song were penned by lead singer Sameer Gadhia, while musically it's a product of the entire band's efforts. It's a light-hearted, sunny piece of alternative rock that evokes beachsides and summertime. Speaking of his lyricism in general, Sameer Gadhia has said that "for me, the lyrics process is a mix of conscious substance and nonsensical spontaneity. Often, I start with one true phrase or line of a song. From there, I extend the phrase into a whole story."
"Apartment" is narrated in a direct voice, preferring to use feelings and thoughts instead of sensory images. It describes the internal monologue of a man walking home from his lover's apartment. While walking along and listening to the distant swell of waves, his mood shifts from being passionately swept up in the zeal of his romance, to weighed down by the inevitable loneliness he senses at the end of the relationship. The song cleverly plays the two sentiments against each other without resolving the singer's feelings one way or another, making for an emotionally nuanced piece of songwriting.
"Apartment" was released as band's fourth single from their self-titled debut. It charted at #21 on the Billboard Alternative charts. The album, Young the Giant, was both the band's first full-length release and their breakout album. On the strength of its singles, the album propelled the band to international fame. Critics praised its strong songwriting and Gadhia's vocal talents, while lamenting the relatively uninspired aesthetic that held back many of the songs. Gadhia said that the general themes of the album were "a feeling of isolation and almost surreal happiness with a lover". This theme is notably well illustrated on this track.
A version of the song remixed by Captain Cuts appears on Young the Giant's 2011 Remix EP.
The band has released an official recording of a life performance of this song. Dubbed the "In the Open Session," the video features a stripped down rendition of the song performed in front of a fog-filled valley.