The State Department is in charge of relations between the U.S. and other countries, particularly diplomatic relations.
State Department documents back to 1990 are on Westlaw (USTREATIES).
Apostille and the Authentication/Legalization of Documents: The State Department's Office of Authentications and Bureau of Consular Affairs each certify certain official documents for use in other countries. For more information, see the "Apostille and Authentication/Legalization of Documents" entry.
Tough Questions: For truly tough questions about State Department materials, call the State Department's library at 202-647-1099.
Treaties: The Department is a good source for information on U.S. treaties. The number for the Treaty Desk is 202-647-1345.