Emblem of Starfleet Security.
Starfleet Security is the branch of the Federation Starfleet responsible for security aboard all Federation starships and at all Federation starbases and outposts. In addition, Starfleet Security is responsible for providing security at all Federation government facilities, such as the Palais de la Concorde. Starfleet Security is responsible for maintaining and enforcing Starfleet regulations, procedures and policies on all Starfleet and affiliated facilities, outposts, and vessels, and is responsible for setting security clearances for all Starfleet and government personnel and facilities. Starfleet Security often works in conjunction with Starfleet Intelligence. ("The Drumhead" [TNG], et. al.)
A special division of Starfleet Security provides constant security for the President of the United Federation of Planets. Members of the presidential protection division are present with the President at all times, and constantly guard the Château Thelian and the Presidential Office. Typically, Security officers are garbbed in a standard Starfleet duty uniform; on special occasions, officers may wear formal wear from their home planets or a Starfleet dress uniform. (Articles of the Federation.)
In 2367, Vice-Admiral Thomas Henry was Chief of Starfleet Security. ("The Drumhead" [TNG].)
In 2379, Starfleet Admirals William Ross, Alynna Necheyev, and Mamoru Nakamura used their authority within Starfleet Command to order all members of Starfleet Security out of the Palais and away from Federation President Min Zife, whom they forced to resign at gunpoint. Subsequently, agents of the nefarious agency known only as Section 31 assassinated Zife, his chief of staff, Koll Azernal, and Federation Secretary of Military Intelligence Nelina Quafina.