This ballad is the lead single from the soundtrack to the movie The Twilight Saga: Breaking Dawn – Part 1 and is performed by American Pop singer Bruno Mars. He penned the tune whilst out on the road and produced it with his Smeezingtons production colleagues, Philip Lawrence and Ari Levine. It was released exclusively on iTunes September 27, 2011.

Mars had already started on the song before he got the call to contribute to the film's soundtrack. After seeing the movie, he thought that it would be "a perfect fit."

Speaking to Billboard magazine, Mars explained that "the Twilight movies, "for me [are] a love story. But it's a dark love story. And I think the best way to describe the song is: it's the darker side of love. I think that pretty much sums it up. 'It Will Rain' started off with me and the guitar, and I just had this melody in my head and basically laid it down after I saw the film."

According to an interview with AP writer Ryan Pearson, Twilight music producer Alexandra Patsavas chose Mars as the film centered on a wedding and, "Who more appropriate than Bruno Mars to write a timeless, classic wedding song?"

Bruno Mars literally turned off the radio when he first heard this song because of his displeasure with its final mix. "I felt like I was a mosquito singing," he told Billboard magazine.

Director Phil Pinto shot the music video in a converted London pub, which finds Mars in a complicated, though non-vampire, relationship. His girlfriend was played by a Portuguese Maxim model, who had trouble warming up to the artist because she was nervous. Mars gave her guitar lessons between takes to make her feel more comfortable. During the volatile scenes, she opted to swear at him in Portuguese because she kept ruining takes by laughing at her own English. The clip also features bits of footage from The Twilight Saga: Breaking Dawn - Part 1.

It actually didn't rain in the video. The "rainwater" on the window was achieved by a guy with a hose.