A '''generation ship''' is a hypothetical that of light (see interstellar travel). Since such a ship might take from as little as below a hundred years to tens or even hundreds of thousands of years to reach even nearby stars, the original occupants might either grow old or die during the journey and leave their descendants to continue traveling, depending on the life span of its inhabitants and relativistic effects of time dilation.

It is estimated that, in order to assure life support), providing food, air, and water for everyone on board. It must also have extraordinarily reliable systems that could be maintained by the ship's inhabitants over long periods of time.

It has been suggested that humans create large, self-sustaining space habitats before sending generation ships to the stars. Each space habitat could be effectively isolated from the rest of humanity for a century or more, but remain close enough to Earth for help.  This would test whether thousands of humans can survive on their own before sending them beyond the reach of help.

Some have compared planets with life to generation ships; this idea is usually called "Spaceship Earth".

==In fiction==

Generation ships are often found in theme is that inhabitants of a generation ship have forgotten they are on a ship at all, and believe their ship to be the entire universe. 

Other examples of fictional generation ships include: 
* The ''Trigun'' anime and manga
*''Captive Universe'', novel by Harry Harrison
*''Non-Stop'' aka ''Starship'', novel by Brian Aldiss 
*''The Dark Beyond the Stars'', novel by Frank M. Robinson 
*''Orphans of the Sky'', novella by Robert A. Heinlein 
*''Book of the Long Sun'', four-novel series by Gene Wolfe 
*''The Starlost'', short-lived 1970s TV series by Harlan Ellison
*''The Star Seekers'', 1953, one of the Winston Science Fiction books for young adults by Milton Lesser
*''The Ballad of Beta-2'', novella by Samuel R. Delany
*''Colony'', novel by Rob Grant
*Original Video Animation ''Megazone 23''
*The ''Rama'' series of books by Arthur C. Clarke and Gentry Lee
* ''Kelvan Multi-Generation Ship'' - from the Star Trek'' episode "By Any Other Name". 
*The ''Star Trek'' episode "For the World is Hollow and I Have Touched the Sky"
*The ''The Disease"
*''James White
* ''Mayflower II'', a novella by Stephen Baxter
* ''The Naked God'', a novel by Peter F. Hamilton
* '' Learning the World: A Novel of First Contact by Ken Macleod
* ''The Exiles Trilogy'', a series by Ben Bova
* "Ship of Fools" by Richard Paul Russo
* ''Nemesis'' by Isaac Asimov
* ''Seed of Light'' by Edmond Cooper
* ''Chasm City'' by Alastair Reynolds
* ''Le Papillon des Etoiles'' by Bernard Werber.
* ''Colony Fleet'' by Susan Matthews
* The 1981 BBC Radio 4 show Earthsearch
* The novella "Paradises Lost" in The Birthday of the World collection of stories by Ursula K. LeGuin
* The Koros-strohna worldships of the Star Wars Expanded Universe are an organic form of generation ship.
* In the ''Enterprise'' becomes a generational ship in an alternate timeline.
* In the computer game ''Elite'' by ''Ian Bell'', although generation ships are never actually seen in the game, they are discussed in the manual and novella included with the game.
*Bruce Sterling's short story ''Taklamakan'' is about a group of Chinese habitats that simulate generation ships in a cave under the Taklamakan desert.
*The oft-lampooned, low-budget film ''Space Mutiny'' takes place aboard a generation ship known as the ''Southern Sun''. 
*The television series ''Firefly'' is set in a far-away planetary system that was colonized by generational ships.
*The Marathon series of video games were based around a Generational Interstellar vessel called the "Marathon". The vessel itself is known as a "Colony Ship" and was converted from the Martian moon Deimos.
*The Sega Genesis video game Phantasy Star III takes place on a generation ship (although this is not revealed specifically until very late in the game).
*Sid Meier's Civilization II allows for the construction of a generation ship (though the in-game transit time can be brought as low as twelve years, much less than what would be required of a generation ship).
*The 1977 science fiction pop music concept album "The Intergalactic Touring Band" features a storyline based on generation ships.
*In the upcoming MMOG Infinity: The Quest for Earth, The Geodesan people construct a massive generation ship named ''IOS - 1'' (Interstellar Operational Spaceship) to carry 1.1 million Geodesans away from their dying star, Delta.
*The first science fiction role-playing game, Metamorphosis Alpha (published 1976), is set on a generation ship whose crew was mostly wiped out, leaving the ship adrift and the mutated occupants unaware that their ship is not the entire world.

'''世代宇宙船'''（'''せだいうちゅうせん'''）は恒星間航行の手段の一つとして考えられている恒星船である。元々はサイエンス・フィクション (SF) によって提唱された概念である。

==概要== 
光速を超えられず、他の恒星系へ行くには数十年ないしそれ以上の時間を要する。そこで都市あるいは国家に匹敵する人口を収容可能な、それ自体居住空間としての機能もそなえた、巨大な宇宙船に多数の男女が乗り組み、船内で子供を産み、育て、初代乗組員の子孫が目的地に到着するのである。

数世代にわたる星間航行を実現させるため、世代宇宙船には考えうるあらゆる事態に対応できるよう、搭載可能な限りの知識が持ち込まれる。これはまた次世代へ母星の歴史を継承するためや、教育のためでもある。また、酸素や水資源などのリサイクル環境も、十二分に配慮されるべきである。あるいは、前世代人の肉体も循環可能な資源とみなされる場合もある。

世代宇宙船の問題点としては、地球から遠く離れ数世代を重ねて航行する世代宇宙船の乗組員たちが、地球人としてのアイデンティティーや、第一世代の持っていた目的意識を継承し続けることは難しいということが挙げられる。SF作品の中には、世代を重ねるうちに自分たちが宇宙船に乗っている事が忘れられてしまい、外の世界の存在を知らないまま飛び続ける話もある。

また、世代宇宙船は地球の文明の進歩から取り残されることになり、その出港後に画期的な超光速航法が開発され、後の宇宙船が追い越してしまうのではないか、という問題もある（ただし、超光速航法は2006年現在の物理学上、理論的に不可能であるが、世代宇宙船はコストや時間を度外視すれば理論的には実現可能である）。