The First Contact Office was a branch present within the United Federation of Planets which was charged with making contact with lesser developed civilizations when they joined the interstellar community. The beings that were in charge of this body were noted as being the keepers of the Prime Directive. (TOS novel: Prime Directive)
As part of their operations, the First Contact Office was known to inflict individuals of the target world with Missing Time Syndrome to ensure that they did not remember encounters with off-worlders. (DS9 - Millennium novel: The Fall of Terok Nor) They were also responsible for removing any evidence of Federation involvement in pre-warp cultures. (TOS novel: Preserver)