Giant-killing or giant killer may refer to:

• Killing a literal giant, such as:
  • Gigantomachy, a Greek mythological battle
  • David and Goliath, a biblical story
  • "Jack the Giant Killer", a Cornish fairy tale and legend
• Upset (competition), occurring when an underdog beats the favourite (or top dog)
  • Underdog, a person or group in a competition who is largely expected to lose
• Giant Killing, a Japanese manga and anime series
• Giant Killer (call sign), an American military aviation call sign
• "Giant Killer" (story), a 1945 short story by A. Bertram Chandler
• Giantkiller, a DC Comics limited series

• Giant Killers (disambiguation)
• Jack the Giant Killer (disambiguation)