The Vulcan Diplomatic Corps (VDC) was an organization that was within the Vulcan government. The position of Ambassador was considered a highly elite position within the VDC.

In 2269, Ambassador Sarek considered making T'Pala, a recently orphaned girl, his protege in the VDC due to her skills in the social sciences as well as her interest in politics. (TOS novel: Mindshadow)

During the year 2373 when the Virogen crisis engulfed numerous worlds in the United Federation of Planets, Spock made use of VDC resources in order to learn more about the suspected murder of his father. However, it was learnt that the organization responsible had infiltrated the Vulcan Diplomatic Corps and were monitoring his actions. (TOS novel: Avenger)

In 2375, Spock once more used VDC resources in order to learn about the mysterious organization called Project Sign but learnt very little of that agency. (TOS novel: Preserver (novel))