"Day 'n' Nite" is a song by American hip hop recording artist Kid Cudi. The song was written and co-produced by Kid Cudi, alongside his longtime collaborator and friend, Brooklyn-based producer Dot da Genius. It was released as Cudi's commercial debut single on February 5, 2008, but had initially leaked online in December 2007, and was featured on several blogs in mid-November 2008.

The single, which was included on his breakout mixtape A Kid Named Cudi (2008), also serves as the lead single from his debut studio album Man on the Moon: The End of Day (2009). The song has since sold over 2,000,000 digital downloads in the United States. The song peaked at number three on the US Billboard Hot 100. The song was ranked at number 15 on the "Best 25 Songs of 2009" list by Rolling Stone and also ranked at number seven on Complex's "100 Best Songs of The Complex Decade".

As a young man Cudi moved from his hometown of Cleveland, Ohio, to Brooklyn in New York City, to pursue a music career. Upon his arrival, he stayed with his uncle. His uncle later kicked him out, which subsequently led to Cudi writing "Day 'n' Nite":

"My uncle that I lived with passed in 2006. We were actually beefing because he forced me out the house when I didn’t have another situation set up, so I was bitter. I never apologized for it, and that kills me. That’s why I wrote "Day 'n' Nite." If he wasn’t there to let me stay with him those first few months, there would be no Kid Cudi. It fucked me up watching him go, but it was like, "I have to fulfill this destiny now for sure." Things were moving but they weren’t solidified yet. I had "Day ’n’ Nite," we were just getting started, and I was like, "This shit has got to pop off." I wasn’t taking no for an answer."

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