Timothy Ross Armstrong (born November 25, 1965) is an American musician, songwriter and record producer. Known for his distinctive voice, he is the singer/guitarist for the punk rock band Rancid and hip hop/punk rock supergroup Transplants. Prior to forming Rancid, Armstrong was in the ska punk band Operation Ivy.

In 1997, along with Brett Gurewitz of the band Bad Religion and owner of Epitaph Records, Armstrong founded Hellcat Records. In 2012, through his website, Armstrong started releasing music that influenced him, along with stripped-down cover songs of his own under the name Tim Timebomb. Armstrong is also a songwriter for other artists. Armstrong won a Grammy Award for his work with Jimmy Cliff and Pink, and has also worked with Joe Walsh and the Interrupters.