末日幻想（英语：Apocalyptic fiction）是科学幻想中幻想由于核战争、瘟疫、外星生命入侵、撞击事件、人工智能叛变、技术奇异点、种族退化、超自然现象、末世论、气候变化、资源枯竭或其他灾害造成文明结束的子类别。末日后幻想（英语：Post-apocalyptic fiction）设定在上述灾难后的世界或文明。时间范围可以是灾难后的不久以后，关注幸存者的痛苦或心理；也可以是一段时间之后，通常描写灾难前文明被遗忘（或被神话）的故事。灾难后文明通常出现在一个农业社会、无技术世界，或者只遗留部分技术的世界。此主题与反乌托邦间的界限十分模糊。

Apocalyptic and post-apocalyptic fiction is a genre which involves global catastrophic risk. The literature is mainly science fiction, science fantasy or horror fiction with the apocalypse event typically being climatic, such as runaway climate change; natural, such as an impact event; man-made, such as nuclear warfare; medical, such as a plague or virus, whether natural or man-made; or imaginative, such as zombie apocalypse or alien invasion. The story may involve attempts to prevent an apocalypse event, deal with the impact and consequences of the event itself, or it may be post-apocalyptic, set after the event. The time frame may be immediately after the catastrophe, focusing on the travails or psychology of survivors, the way to maintain the human race alive and together as one, or considerably later, often including the theme that the existence of pre-catastrophe civilization has been forgotten (or mythologized). Post-apocalyptic stories often take place in a non-technological future world, or a world where only scattered elements of society and technology remain.