Starbase 21
Starbase 21 was a Federation starbase administered by Starfleet. The starbase was located in the Alpha Quadrant. Systems near this starbase included the Xahea system, the Algol system, and the Thalos system.

In 2259, the location of this starbase was labeled on a stellar cartography chart that was seen on the 's ready room viewscreen. ()

In 2270, this was the destination of the  after its encounter with Kukulkan. ()

In 2399, the location of Starbase 21 was labeled on a Federation star chart in Fleet Admiral Kirsten Clancy's office at Starfleet Headquarters. This base was located in neutral space. () 

In 3189, the location of Starbase 21 was denoted on a holographic star chart of the galaxy at Federation Headquarters. ()

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bg:Звездна база 21
de:Sternenbasis 21
fr:Base stellaire 21
nl:Sterrenbasis 21
0021, Starbase