Admittance into the Federation is granted either by invitation or by successful petition submitted by a world, civilization, or government wishing to join voluntarily. In the latter case, membership is granted only upon the meeting of certain requirements and conditions. The government of the prospective member must submit an official petition to the Federation Council, outlining its desire to join. A thorough and lengthy investigation of the prospective member's culture will follow, including copying records from the applicant's central computer. This investigation often lasts for several years, and is designed to ascertain whether or not the culture genuinely shares the values of the Federation: the values of benevolence, peaceful coexistence and cooperation; the rule law, justice, equal rights and freedoms.

Before an investigation even begins, a prospective member has to meet the following requirements:

• An advanced level of technology, with a baseline definition being the capability of faster-than-light space travel.
• The government has achieved a stable planetary of political unity, demonstrating a resolution of social and political difference, and a respect of the rights of the individual.
• No form of caste discrimination is practiced.

Every prospective member has to go through the same admittance process, which includes a specific time table. This time table can be shortened if the prospective member successfully negotiates such, but this is rare.

Individual groups are able to give up their status as Federation citizens, which happened with the settlers of Dovan V elected to remain on their world when it was ceded to the Cardassians. In the mid-2380s, 14 members of the Federation threatened to secede in opposition to Starfleet's plan to assist the Romulan Star Empire evacuation ahead of the Romulan supernova. In 2401, the Borg was granted provisional membership to the Federation under the leadership of a Queen from an alternate timeline who had merged with Dr. Agnes Jurati and sought to create a better Borg Collective.

While withdrawing from the Federation and giving up membership is possible, an unconditional and immediate withdrawal in not possible, and it requires a lengthy process with certain requirements to be met before withdrawal.