The United Federation of Planets (abbreviated as UFP and commonly referred to as the Federation) was a supranational interstellar union of multiple planetary constituent political entities under a single central government, founded on the principles of liberty, equality, peace, justice, and progress, with the purpose of furthering the universal rights of all sentient life. Federation members exchange knowledge and resources to facilitate peaceful cooperation, scientific development, space exploration, and mutual defense. (TOS: "Arena", "A Taste of Armageddon", "Spectre of the Gun", "And the Children Shall Lead"; DS9: "Battle Lines"; VOY: "Innocence"; Star Trek: First Contact)
Additional nomenclature used to describe the Federation included: "Earth Federation" in TOS: "Friday's Child" and TAS: "The Lorelei Signal", "Federation of Planets" in TOS: "A Piece of the Action", and "United Fleet of Planets" (incorrectly, by Lokai of the planet Cheron) in TOS: "Let That Be Your Last Battlefield".
One of the most powerful interstellar states in known space, it encompassed eight thousand light years. The total number of formal member worlds was over one hundred and fifty in the 24th century (Star Trek: First Contact). At its height, at an unstated time between the 25th and 31st century. it numbered three hundred and fifty members (DIS: "Die Trying"). Unlike its imperial rivals – especially the Klingon Empire and the Romulan Star Empire – who derived power from a single species subjugating other races. (TOS: "Errand of Mercy", "A Private Little War"; Star Trek Nemesis; ENT: "United"), the Federation's various member worlds joined voluntarily and were equals in the Federation's democratic society (TNG: "Attached"; DS9: "Emissary", "Rapture"; VOY: "The Void"; DS9: "Paradise Lost"; VOY: "Author, Author").
Starfleet was incorporated to maintain exploratory, scientific, diplomatic, and defense functions (TOS: "The Cage", "Where No Man Has Gone Before", "Journey to Babel").
In the alternate reality, Captain Christopher Pike described the Federation as a "peacekeeping and humanitarian armada." (Star Trek)
Federation culture, values, and technology had vast influence; across space and time, as well as other dimensions and subspace domains. Encountering numerous clashing ideologies, some conflicts escalated into significant resistance, such as armed conflict, and even temporal incursions intended to prevent key historical events from occurring.