State Dept. Foreign Relations of the US
The Foreign Relations of the United States series of volumes is published by the State Department, using records from a wide variety of government sources. These volumes are typically published a few decades after the period covered, in order that much of the record be declassified and available for use in these studies.
These volumes include Vietnam foreign policy for 1962-1964, as well as volumes on Cuba and US-Soviet relations. There are some notable absences from the records encoded in them; for instance, the proceedings of the 8th Secretary of Defense Conference on Vietnam, held in May of 1963, were not declassified until late 1997, thus too late for inclusion in the relevant Vietnam volumes which were published in 1991.