"Kryptonite" is a song by the American rock band 3 Doors Down. It was originally released as a demo for local play by 97.9 WCPR-FM in Biloxi, Mississippi. The song first charted on the Mainstream Rock Tracks chart reaching number-one for 9 weeks, then it hit the Modern Rock Tracks also staying at number-one for 11 weeks, being one of the longest-running songs on the chart. It also reached number one on the Pop Songs chart for 5 non-consecutive weeks, peaked at number 4 on the Adult Top 40 chart and number 3 on the Billboard Hot 100, being the band's highest-charting single there.

The song was written by drummer/vocalist Brad Arnold in a mathematics class when he was fifteen and was one of the first songs he ever wrote.

In terms of the song's meaning, Arnold has said:

Directed by Dean Karr, the music video presents an old man who was a big-time action hero on 1950s TV. The scene cuts between the band hanging around on the roof of the apartments where the old man lives, spying on a man harassing a woman. When the man drags her away, the old man dons his trusty suit and follows. In between shots of the old hero chasing the bad guy and failing to protect himself against a group of goths, the band is shown playing in a club with several other elderly people dressed as caricatures of comic villains. The video comes to a close when the old man dives through the skylight and catches the bad guy off guard, possibly knocking him out by falling on top of him. The video ends with the old man smiling, giving a thumbs up to the camera.

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