"Case of the Ex" (sometimes subtitled "Whatcha Gonna Do"[1]) is a song performed by American singer Mýa.

It was written and composed by Christopher "Tricky" Stewart (with his songwriting partners Traci Hale and Thabiso "Tab" Nkhereanyne) for Mýa's sophomore studio record, Fear of Flying (2000).

The song received generally mixed reviews from contemporary music critics and was Mýa's breakthrough hit, both stateside and internationally.

Mýa worked with choreographer Tina Landon, who later won an American Choreography Award for Best Hip Hop music video.

The video, filmed in the barren Mojave Desert, featured the singer and her backup dancers performing with large poles as props and dancing in the sand.

The visuals drew comparisons to Janet Jackson's "You Want This" (1994) music video and Mel Gibson's 1979 film Mad Max.

"Case of the Ex" was composed by Christopher Stewart, Traci Hale, and Thabiso "Tab" Nkhereanyne in late 1999.

[3] Initially, Mýa was working at the Redzone Studios in Atlanta, Georgia, when she heard an early instrumental of the song through the walls from the room next door.

[4] Originally a rap song, Stewart heavily rearranged the track to make it fit Mýa's persona.

"[2] It was Hale who came up with the lyric idea, which was inspired by a relationship she was going through at the time and revolved around "a strong woman who won't tolerate her man returning to his ex-girlfriend.

"[6] Jacqueline Springer of NME gave the song a favorable review and rated the single seven out of ten stars, writing: "No-good boyfriend anthem number four thousand eighty time, y'all [...] The stuttering arrangement of the original is cool and suits Mýa's brooding mood, but after a while it simply sits in the wind — there's no real build into a bassline leaving the track to run along a continuous pop/r&b vibe [...] Anyway, we all know what to do when ex-girlfriends re-emerge don't we?

[8] "Case of the Ex" was featured on The Village Voice's Pazz & Jop end of the year critics list.

"[24] During filming, a wardrobe malfunction had occurred on set where the studs Mya and her dancers wore didn't have lining on the opposite sides, causing the crew to get cut up on their skin, while simultaneously getting sunburnt with sand getting in their sunburns and scrapes.

"[24] "Case of the Ex" music video "opens in a Mad-Maxish desert setting, where a posse of well-muscled girls stands before a group of somewhat nonplussed boys".

[35] British girl group IV Rox re-recorded "Case of the Ex" and released it as their debut single.

[41] Writing for Pitchfork, Marc Hogan suggested "Case of the Ex" as one of his choices for his 6 Millennium Era Hits That Top 40 Needs to Sample list, commenting, "A clear-voiced young singer with a strong sense of identity like Kehlani (or maybe Halsey in a pinch) could work wonders here.

[44] In January 2024, Rolling Stone magazine ranked "Case of the Ex" as one of their "The 100 Greatest R&B Songs of the 21st Century" list.