Apocalyptic and post-apocalyptic fiction is a subgenre of science fiction in which the Earth's civilization is collapsing or has collapsed. The apocalypse event may be climatic, such as runaway climate change; astronomical, such as an impact event; destructive, such as nuclear holocaust or resource depletion; medical, such as a pandemic, whether natural or human-caused; end time, such as the Last Judgment, Second Coming or Ragnarök; or any other scenario in which the outcome is apocalyptic, such as a zombie apocalypse, cybernetic revolt, technological singularity, dysgenics or alien invasion.

A global catastrophic risk or a doomsday scenario is a hypothetical event that could damage human well-being on a global scale, even endangering or destroying modern civilization. An event that could cause human extinction or permanently and drastically curtail humanity's existence or potential is known as an "existential risk."