Colony
In interplanetary terms, a colony was a settlement on a planetary body of non-indigenous peoples, usually sponsored by a spacefaring species or government. 

Colonies were generally – though not always – established on worlds devoid of native sentient life and could be specialized for various purposes such as research, agriculture, detention, commerce, mining, or leisure. (;  et al.). Typically, colonies were situated on or below the surface of a planet or moon. (; ;  et al.).

Types of colonies

Federation 
In the Federation, most colonies began small, often consisting initially of only a few hundred settlers. Over time, some of these colonies expanded and grew to support a significantly larger population. (; ; ; )

The Federation Council had to grant permission before a formal settlement was established on any planet. Finding planets suitable for colonization and successfully placing settlers on them was a major goal of the Federation. To increase habitability, colonization could also be preceded by terraforming and/or the use of a weather control system. The Federation usually tasked Starfleet with the logistic requirements of terraforming as well as the delivery of colonists, often in waves, and shipping integral infrastructure such as residential pods, schools and hospitals. 

Sometimes, however, Starfleet had to forcibly relocate settlers because of threats to the colonists' survival or because the Federation had surrendered control of a colony planet. A notable example of the latter occurred during the swap of many colonial planets (such as Dorvan V with the Cardassians as part of a treaty to effect an end to a prolonged border war. Many of the colonists refused to allow the distant Federation government give Starfleet the power to enforce the treaty and instead renounced Federation citizenship, banding together in a loose coalition known as the Maquis. (, ; )

Others 
In some cases, spontaneous, unintended colonies developed when an accident stranded spacefarers on a planet. While not technically colonies in the formal, planned sense, these "settlers" often thrived nonetheless. In other cases, settlements-come-colonies arose when enthralled peoples overthrew their captors and established equally unintended "colonies". A rather unusual case arose when Captain Kathryn Janeway and Commander Chakotay contracted a terminal illness that forced them to remain on a planet, which they christened "New Earth" and had planned to settle until the  crew returned for them after obtaining a cure from the Vidiians. (; )  

In 2369, the Rakhari Croden told Odo about a Changeling colony on an asteroid in the Chamra Vortex. ()

While exploring the Gamma Quadrant, a ship of Klingons found that  was not worthy to be a Klingon colony, but they took several energy spheres aboard. ()

See also

Lists of colonies 
Links to articles with lists of many colonies:
:Category: Colonies
Bajoran colonies
Federation colonies

Other cases 
The lists in the following articles also contain colonies as well as planets that might be considered colonies:
Klingon planets
Cardassian planets
Demilitarized Zone: a region separating Federation and Cardassian space that contained numerous colonies from both parties

Appendices

Background information 
For determining sizes of interplanetary governments, it is unclear whether colonies were considered mere extensions of their parent government's home-worlds or retained a degree of independence and were considered (full or partial) member worlds. This is particularly well-illustrated by the question of the number of "full members" of the Federation. The Federation's size of 150 members given in  suggests the former applies; otherwise, the number would almost certainly be much larger. The "complete list" in Star Trek: Star Charts of Federation member worlds includes several colonies, suggesting that at least some of these were responsible for their own local government and retained a form of autonomy, as well as a degree of Federation membership. It is possible that given their nature as settlements of Federation citizens, certain colonies were granted automatic or at least an easier path to membership – as opposed to the usual lengthy application procedure (with its several pre-conditions) for would-be Federation members, demonstrated by Bajor's somewhat Byzantine application process. Other non-canon sources, such as the official  website give a figure of least 120 members and 700 colonies as of 2258, though this provides neither an indication of whether any of the members were initially colonies nor if any existing colonies had member status. (See size and location of the Federation and Federation members.) 

With other governments, such as the Klingon Empire and Romulan Star Empire, similar uncertainty exists. While both had established a number of respective Klingon and Romulan outposts and colonies, both also had control of several conquered planets. As with the Federation, it is not known whether their colonies, or at least some of them, had the same status as their subject planets.

Related topics 
 Colony ship
 Penal colony
 Scientific colony

External links 
 
 

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Settlement types