Cataclysm is derived from the Greek katá (κατά), 'down, against', and klyzō (κλύζω), 'wash over, surge'. It may refer to:

• Generally, any large-scale disaster
• Deluge (mythology)
• Doomsday event, see hypothetical risks to civilization, humans, and planet Earth
• A catastrophic natural event:
  • List of geological phenomena
  • earthquake, the result of a sudden release of energy in the Earth's crust that creates seismic waves
  • volcanic eruption

• World of Warcraft: Cataclysm, an expansion pack of Blizzard Entertainment's World of Warcraft
• Cataclysm: Dark Days Ahead, an open-source cross-platform roguelike video game
• Homeworld: Cataclysm, a stand-alone expansion, of the Homeworld space-based RTS franchise

• Cataclysm (Dragonlance), a fictional event in the Dragonlance novels
• Batman: Cataclysm, a DC Comics crossover story arc featuring Batman
• Cataclysm: The Ultimates' Last Stand, a 2013–2014 crossover storyline appearing in the Ultimate Marvel line of books
• Godzilla: Cataclysm, a miniseries from the Godzilla comics by IDW Publishing, see Godzilla (comics)#Miniseries

• A special ability used by Cat Noir, a character in Miraculous: Tales of Ladybug & Cat Noir
• "Cataclysmic", a song by Joe Satriani from the 2015 album Shockwave Supernova

• Cataclysmic variable star, which irregularly increases in brightness by a large factor, then drops back down to a quiescent state (initially called nova)
• Cataclysmic pole shift hypothesis, pseudo-scientific claim of past rapid changes of Earth's axis
• Ekpyrosis, a conflagration
• Pyroclastic flow, fast-moving current of hot gas and volcanic matter
• Lahar, violent volcanic mudflow or debris flow
• Eschatology, part of theology concerned with the final events of history
• Kataklysm, Canadian death metal band