"Back That Azz Up" (edited version titled "Back That Thing Up") is a 1999 hit single by Juvenile for Cash Money Records, his biggest hit from his 1998 album 400 Degreez. The song, an explicit exploration of the same themes as Sir Mix-a-Lot's "Baby Got Back" was Juvenile's biggest hit single until the release of "Slow Motion" in 2004. The song has been covered by a number of artists from Darwin's Waiting Room to New Found Glory.

Also performing verses on "Back That Azz Up" are the song's producer, Mannie Fresh, and Juvenile's fellow Hot Boy Lil' Wayne. Wayne's verse ("After you back it up and stop/then drop, drop, drop, drop it like it's hot") popularized an expression for a certain type of sexually suggestive dance; the expression was later re-popularized by Snoop Dogg with his number-one hit "Drop It Like It's Hot".

Both the song and its music video were omnipresent in media venues for much of 1999 and early 2000. "Back That Azz Up", Juvenile's "Ha", and B.G.'s "Bling Bling" were the three hits that launched Cash Money into the pop mainstream.