This was written by Brandy together with Rodney Jerkins, LaShawn Daniels, Fred Jerkins III and Japhe Tejeda. The song's lyrics tell a story about two women disputing the love of a man. They were inspired by Paul McCartney and Michael Jackson's 1982 duet "The Girl Is Mine," and by The Jerry Springer Show, where love triangles among the guests were a common theme.

In real life, there was no boy that Brandy and Monica were fighting over - the story was completely made up. The song exploited the persistent rumor that Brandy and Monica were locked in a genuine feud. "We didn't even know each other," Monica explained in 1998. "I had never even seen her before because I listen to a lot of gospel music. From the the time she was [first] released and I was [first] released, instantly people compared us and I never understood it. It's like they chose the two of us out of the bunch to put at odds. They never did it with me and Aaliyah, or Brandy and Aaliyah. It was always Brandy and Monica. That's why we took the song and brought humor to a situation that people tried to make serious. We thought it would be really funny to show us feuding in the video and then come together at the end, because we wanted people to let go of the idea of us not liking each other - but of course, they haven't."

Originally Monica and Brandy recorded the song together in Los Angeles. However the joint recording was felt to be a failure so Monica rerecorded her vocals separately in Atlanta under producer Dallas Austin, who also worked with popular trio TLC on songs like "Creep" and "Unpretty." Austin told Billboard: "I had to make Monica Monica on it. I didn't want it to turn into something where Monica's full character wasn't on it. It had to have their attitudes on it, and not just be them singing a song."

The song spent 13 weeks at #1 in the US, making it the all-time #1 female duet in US chart history and the top-selling US single in 1998 with over 2 million copies sold. It topped the Canadian charts for 15 weeks.

The Hot 100 success was aided by a Billboard rule making songs that weren't sold as singles in the US ineligible for the chart - a stipulation that was lifted later in 1998. This kept "Torn" by Natalie Imbruglia and "Iris" by the Goo Goo Dolls - both not sold as singles - from competing on the chart.

This won the 1998 Grammy for Best Rhythm & Blues Performance by a Duo.

Prior to the release of this song, R&B had not been a popular musical genre in Asia. "The Boy Is Mine" changed that when it topped the Asia Hitlist for eight weeks).

In the music video, directed by Joseph Kahn, the girls are neighbors fighting over their shared boyfriend, played by Mekhi Phifer.

Brandy and Monica sang this at the MTV Video Music Awards in 1998. It was the only time they performed the song on television together.

Amber Riley and Naya Rivera sang this on Glee in the 2010 episode "Laryngitis."