The Federation Starfleet, also known simply as Starfleet or Star Fleet, was the exploratory and defensive force of the United Federation of Planets. Starfleet's function was to explore unknown territory on the behalf of the Federation government, to defend the Federation and its allies from threats, to further Federation policies and interests throughout interstellar space, and, when applicable, to initiate first contact with newly-discovered worlds and to engage in diplomatic negotiations on the behalf of the Federation. As per its mandate of deep-space exploration, its personnel were frequently brought into contact with cultures and sentient species whose existences were unknown to the Federation. Starfleet officers therefore acted as official representatives of the Federation in these cases. Starfleet vessels were also frequently used to ferry ambassadors on diplomatic missions.
Main Article: Starfleet History
The Federation Starfleet was chartered in 2161 with the founding of the Federation. A charter was written and an institution for the training of the Federation Starfleet officer corps, Starfleet Academy, was established. The Federation Starfleet was created from the space and science programs and militaries of the Federation's founding Member States, including the United Earth Starfleet (founded only about twenty to thirty years earlier), the Andorian Imperial Guard, and the Vulcan, Tellarite and Alpha Centauri military forces. Starfleet Headquarters, the primary hub of Starfleet Command, was built near the Presidio in San Francisco on Earth, as the United Earth Starfleet Command complex had been, as was the Academy. 
After the destruction of the Borg Collective, Starfleet had lost forty percent of its fleet.
By the year 12263, Starfleet was called Universal Fleet.
Senior Officers Edit
The senior-most officer of Starfleet was the Commander-in-Chief of the Federation Starfleet (C-in-C), who served as a military advisor to the Federation President and Council, and had operational authority over the whole of the Federation Starfleet.
Beneath the C-in-C was the Commanding Officer, Starfleet Command, who was the Starfleet flag officer who commanded Starfleet Command.
The Chief of Staff for the Federation Starfleet ranked below the Commanding Officer, Starfleet Command, but did not report to that officer in all matters. Free Agents fell under this officer's authority.
The Federation Starfleet Liaison to the Office of the President was responsible for communicating and coordinating with the President of the United Federation of Planets, reporting to the President regarding the activities of Starfleet and the orders of the C-in-C, and relaying the President's orders back to Starfleet.
A symbol of Starfleet is sometimes included in the uniform wear of Starfleet personnel, although some uniform designs forgo any Starfleet symbol badge with instead a marking depicting the individual assignment or mission of the wearer.
In the early days of the Federation, Earth Starfleet personnel wore uniforms with a patch Starfleet insignia on the right shoulder and an assignment patch on the opposite shoulder.
By the 2230s, some Starfleet personnel wore a delta-shield shaped embroidery. The delta-shield shape had been devised based on Zefram Cochrane's graphed equation of warp fields, and had previously been used as a symbol by UESPA on the Friendship One space probe. Crew assigned to USS Kelvin wore an outline of that insignia on their uniforms.
By the uniform designs of the 2240s, Starfleet personnel wore assignment insignia based on their vessel assignments. Some such mission patch designs included the delta shield, and Starfleet also adopted a more stylized version of the insignia, elongated and presented sideways as it had been on the Earth Starfleet's patch, in the pennant designation of fleet vessels. This version was also used in some vessels' assignment patches.
In the 2270s, Starfleet Command adopted the mission patch of the USS Enterprise as the insignia for its own assignment patch and as the symbol of Starfleet on vessel pennants. Individual mission patches fell into disuse a few years later, with all personnel adopting the delta shield as their badge of uniform.
The badge would be utilized as a communicator badge in the 24th century, and redesigned as the various communicators used in the 2350s, 2370s and eventually, the 2380s.