Starfleet boasts a wide diversity of species as members. While dominated by individuals from Federation member worlds, Starfleet also has personnel from allied and independent worlds via sponsored Academy applicants as well as the Officer Exchange Program.
Details on individual species may be found by following the link to the Memory Alpha archive.
All citizens of United Federation of Planets member worlds are eligible to apply to attend Starfleet Academy. For worlds that maintain their own planetary government security forces, members of those forces are also eligible to participate in the Officer Exchange Program.
The following species are from the founding member worlds of the Federation or worlds that joined the Federation shortly after its founding in 2161.
The following species are from worlds that joined the Federation in the 23rd Century.
The following species are from worlds that joined the Federation in the 24th Century.
Individuals from a world that is not a member of the United Federation of Planets are also eligible to join Starfleet. Such individuals must usually seek sponsorship from a command-level Starfleet officer. Members of the military or security forces of some worlds are also sometimes able to participate in the Officer Exchange Program.
Individuals from worlds or polities that are formal allies of the Federation may join Starfleet through sponsorship to attend Starfleet Academy, or through the Officer Exchange Program if they are a member of their government's military or security forces.
Individuals from non-aligned worlds and polities are only eligible to join Starfleet through sponsorship to Starfleet Academy by a command-level Starfleet Officer. Examples of this include:
Defectors or asylum seekers from hostile governments and organizations are also allowed to join Starfleet under rare circumstances. One notable example of this are Liberated Borg drones from unknown species.
Artificial life forms are permitted to apply to Starfleet Academy so long as they have been recognized as independent, fully-sentient beings and are sponsored by a command-level Starfleet Officer, and with the approval of Starfleet Command. Examples of these include: