Songfacts®:

• Charli XCX released the thunderous "Boom Clap" in 2014 when she was best known as a writer for other artists and for providing the irrepressible hooks on Icona Pop's "I Love It" and Iggy Azalea's "Fancy." The song landed on the soundtrack of the 2014 romantic comedy-drama movie The Fault in Our Stars and was released as a single, giving Charli her first hit as a lead artist.
  
  "The scene that ['Boom Clap'] is in is an uplifting moment in the film," XCX explained to Billboard magazine. "And while the song itself is very euphoric and enthusiastic about romance... it's about wanting to fall in love, but there's this hint of sadness in that, which I like."
• Charli penned the tune with Patrick Berger, her collaborator on "I Love It." She explained the inspiration to Entertainment Weekly: "We had been listening to loads of French yé-yé pop and the Flying Lizards and Bow Wow Wow, and we were saying how all those songs have dumb, hooky, shouty choruses. They're all sort of childlike. So we wanted to make a song like that."
• The song celebrates epic love. "Being totally immersed in passion and feeling really safe and really alone with that person," Charli explained to MTV UK. "Although I always hear a tinge of sadness in it, that song has quite an acute feeling."
• The Sing J. Lee-directed video features Charli XCX traipsing through the Amsterdam city. The singer explores the same spots that were featured in The Fault in Our Stars movie.
• Charli XCX and Patrick Berger wrote the song during the sessions for her 2013 debut album, True Romance. It didn't make the final cut and was then offered to Hilary Duff to record.
  
  Berger had worked with Hilary Duff before, and Charli was very excited to land a song on Duff's album, but it didn't happen.
  
  "My number one project as a songwriter is to write for Hilary Duff, so when I heard about this, I was like, 'f---k! Are you serious?! This is my 'in!,'" she told MTV UK. "I'm going to make a Hilary Duff album!' So we sent over 'Boom Clap,' but they came back and were like, 'this isn't cool enough for Hilary."
  
  "I was like, crushed," Charli added, sighing. "I thought I was a cool writer, but maybe I'm not. Hilary didn't want my song. What a life-ruiner."
  
  Once Duff declined the offer, XCX decided to use the song as her contribution for The Fault in Our Stars. A few months later, "Boom Clap" also appeared on Charli's second album, Sucker.
• If you think this song has a dumb chorus, you're right - at least according to Charli. She says that it is dumb, but some of the best pop songs have one-line, catchy choruses.
• Charli XCX recorded a version of both this song and "Break The Rules" in Japanese to promote the Japanese release of Sucker. "Boom Clap's" onomatopoeic title stayed the same, but the English words elsewhere were translated. "I did it phonetically," Charli recalled to Digital Spy. "I don't actually remember it now; it was more just me repeating the sounds. But I'm very happy with it, I've always been inspired by Japan constantly, so I kind of wanted to do something for the Japanese fans."