Songfacts®:

• "1999" finds Charli XCX and Australian singer Troye Sivan celebrating turn-of-the-millennium pop culture.
  
  I just wanna go back, back to 1999
  Take a ride to my old neighborhood
  I just wanna go back, sing "Hit me baby, one more time"
  Wanna go back, wanna go
  
  Charli XCX was 7 years old in 1999; Sivan, who was born in 1995, was too young to really remember the period. Charli told Genius that she was a fan of the Spice Girls (especially Baby Spice) and was also "just beginning to get into Britney Spears," as 1999 was the year "...Baby One More Time" was released in the UK.
• The song contains a number of nostalgic lyrical references to the titular year.
  
  Yeah, I just wanna go back
  Nike Airs, All That
  CD, old Mercedes
  Drive 'round listening to Shady like, oh
  
  So why 1999? Charli explained: "There's so much cool imagery around that time period."
  
  She added there was also plenty "to play with, with music videos and fonts and stuff."
• Charli told Billboard she had "vaguely" been looking for a suitable vehicle to collaborate with Troye for a long time and they'd been sending stuff back and forth. When she played him this song he immediately jumped at the idea of collaborating.
• Charli XCX originally wrote the song in LA at Max Martin's compound studio with two Swedes: Writer-producer Oscar Holter (Katy Perry's "Bon Appetit," Hailee Steinfeld's "Love Myself") and singer-songwriter Noonie Bao (Camila Cabello's "Never Be the Same," Rita Ora's "Let You Love Me").
  
  They then sent it to Max Martin, who suggested they change the lyric in the chorus to "I just wanna go back, sing 'Hit me baby one more time.'" Charli said it was a genius idea as "he not only made the song better, but he also referenced himself in a song he and wrote and produced that was big in 1999. I was like, 'That's why he's the king of pop.'"
• The official music video which stars both artists is jam-packed with nostalgic references to 1999 music, film and technology. XCX directed the clip alongside Ryan Staake (Diplo, J.Cole).