The Federation Diplomatic Corps (sometimes referred to as the Federation Diplomatic Corps Service Bureau and as the Federation Diplomatic Office) is the division of the Federation Department of the Exterior which is responsible for negotiating treaties with foreign states and maintaining inter-state relations and diplomacy within the Federation.
Overview
It is composed of Federation ambassadors, and executes the foreign policy set by the Federation President, Federation Council, and Federation Secretary of the Exterior. The Diplomatic Corps often works closely with the Federation Starfleet.
The Federation Diplomatic Corps are widely considered to be obstinate and an impediment to the effective implementation of foreign policy by many in the Federation government and Starfleet. Nontheless, its negotiating skills have proven invaluable in maintaining relatively good relations with many foreign states. (TNG movie: Star Trek: Insurrection; SCE eBook: Interphase, Part One; ST novel: Articles of the Federation, et. al.)
This division grants diplomatic immunity for many ambassador-grade emissaries and dignitaries, including those of normally hostile governments conducting relevant business with the Federation. However, it is uncommon for military officers to be accorded immunity. A corollary to this immunity ensures safe passage within Federation space. (FASA RPG module: Star Trek IV Sourcebook Update).
Diplomatic Corps members are not issued Starfleet combadges. (TNG novel: A Time for War, A Time for Peace)
History
In 2285, the Diplomatic Corps began a major initiative to create a treaty to prevent the proliferation of Genesis Device technology by the other interstellar states who suspected to use the technology of Project Genesis as a weapon of war. (TNG novel: The Genesis Wave, Book One)
The peace negotiations in 2293 with the Klingons saw the Diplomatic Corps. represented by Curzon Dax and Peter Kirk (DS9 episode Blood Oath; TOS novels Sarek and The Last Roundup).
Curzon Dax knew a female member of the Diplomatic Corps. Jadzia Dax talked to her in 2372, and she told her of Federation worlds near the Klingon border were calling for preemptive strike on the Empire. (DS9 episode: "Broken Link")
Just before the USS Enterprise-E visited Ba'ku in 2375, the Diplomatic Corps were busy negotiating with the Dominion. (TNG movie: Star Trek: Insurrection)
In the early 25th century, the Corps was still going strong, with people like Jiro Sugihara assigned by the service to the Earth Spacedock. (STO video game: Star Trek Online)
Divisions
Security Division
The Security Division handled matters of protection of the ambassadorial delegates. (TOS novel: Best Destiny)