The Bureau of Interplanetary Affairs was a Federation department that oversaw the relations between the Federation and independent or member planets. In order to do this, the bureau had a staff of ambassadors who were skilled negotiators.
The bureau was based in an eighty-story skyscraper located in the city of Pil Stornom on Rigel IV. In 2293, the director of the bureau was Lanitow Irizal, and amongst the many ambassadors working for the bureau were Spock and Alexandra Tremontaine. (TOS - Crucible novel: The Fire and the Rose)