Colony

A Colony is a permanent habitation by sentient beings.

Survival of human civilization
The primary argument that called for colonization as a first-order priority was as insurance of the survival of humanity by developing alternative locations off Earth where humankind could continue in the event of natural and man-made disasters or attacks by off-world species [1].

Survival of the biosphere
 Many of the same risks to humankind would destroy parts or all of Earth's biosphere as well. An example would be a very large asteroid impact. But even if these threats are averted, eventually Earth will become uninhabitable.

Vast resources in space
 Resources in space, both in materials and energy, are enormous. The Sol System alone has enough material and energy to support numbers of humans, anywhere from several thousand to over a billion times that of the pre astro Earth-based human population. In the Milky Way there are anywhere up to several hundred billion other star systems. Outside the Milky Way there are up to several hundred billion other galaxies in the universe.

Expansion with fewer negative consequences
 Expansion of sentients and technological progress has usually resulted in some form of environmental devastation, and destruction of ecosystems and their accompanying wildlife.

Could help Earth
 Another argument for space colonization is to mitigate the negative effects of overpopulation.

Other arguments
 Additional goals cite the innate drive to explore and discover, a quality recognized at the core of progress and thriving civilizations. Also cited is the freedom to establish colonies with different ethnic backgrounds, religious beliefs and alternative ideas about political leadership.

Main Types
 Surface-based examples that would exist on or below the surfaces of planets, moons, etc.

 Space habitats — free-floating stations that would orbit a planet, moon, etc. or in an independent orbit around a sun.

History
 For Human post ascent colonization history, see Second Exodus