Three Days Grace is a Canadian rock band formed in Norwood, Ontario, in 1992 originally as Groundswell. Groundswell played in various local Norwood backyard parties and area establishments before disbanding in 1995 and regrouping in 1997 under its current name.

Based in Toronto, the band's original line-up consisted of guitarist and lead vocalist Adam Gontier, drummer and backing vocalist Neil Sanderson, and bassist Brad Walst. In 2003, Barry Stock was recruited as the band's lead guitarist, making them a quartet. In 2013, Gontier left the band and was replaced by Walst's younger brother Matt Walst, who was previously the lead singer of My Darkest Days. In 2024, Gontier officially rejoined the band with Walst also remaining as a singer, making them a two-vocal band, as well as a quintet for the first time since their genesis as Groundswell.

Currently signed to RCA Records, they have released seven studio albums: Three Days Grace in 2003, One-X in 2006, Life Starts Now in 2009, Transit of Venus in 2012, Human in 2015, Outsider in 2018 and Explosions in 2022. The first three albums have been RIAA certified 2× platinum, 3× platinum, and platinum, respectively, in the United States. In Canada, they have been certified by Music Canada as platinum, triple platinum, and double platinum, respectively. In the United Kingdom, their second album One-X was certified silver by the British Phonographic Industry. The band has 17 No. 1 songs on the Billboard Hot Mainstream Rock Tracks chart and 3 No. 1 hits on Alternative Songs.