"The Foreign Relations of the United States series presents the official documentary historical record of major U.S. foreign policy decisions that have been declassified and edited for publication. The series is produced by the State Department's Office of the Historian and printed volumes are available from the Government Printing Office.
FRUS begins with the administration of Abraham Lincoln in 1861. There are two cumulative indexes covering 1861-1899 and 1900-1918. The organization of FRUS is generally chronological, but the dates of the volumes do not necessarily reflect the dates of documentary history. For example, the volumes for 1900-1918 do not include the records dealing with World War I or the Russian Revolution. Each volume has a subject and author index. There is also typically a table of sources and abbreviations at the beginning of each volume.
Many volumes published since 1945 are available online on the State Department website that is maintained by the University of Illinois at Chicago. A full description of Foreign Relations of the United States, including a listing of the online FRUS volumes, is available from the Office of the Historian website..." [From, "About Foreign Relations of the United States," University of Wisconsin Digital Collections Center.
Finally, official documents are compiled, edited and published following a roughly 30-year timelag, although supplementary volumes covering specific years or time frames are occasionally issued out of chronological order.