The Serial Set probably can be considered the single greatest publication series of the U.S. Federal Government. It also arguably can be considered the single most important collection of primary source material for the study of U.S. history for the 19th century and most of the 20th century.
Still being published in paper form in the 21st century, the modern Serial Set is now almost exclusively a collection of Congressional reports and documents. However, for most of its history, it was much more than that, including hundreds of thousands of reports in a wide variety of subject areas from dozens of government agencies.
Coming into existence with the 15th Congress (1817), the Serial Set developed into the Federal Government's archival record of the growth of the young nation, covering social conditions, scientific advancements, Western and foreign exploration, international relations, geology and natural resources, economic policies, census counts, and more. Works on such major topics as slavery, the Civil War, and relations with Native Americans are invaluable. The 13-volume set Affairs in the Late Insurrectionary States; The Ku-Klux Conspiracy appeared in 1872 in the Serial Set. About 100 years later, author Dee Brown conducted much of his research for his book Bury My Heart at Wounded Knee in material in the Serial Set.
As the nation and government grew in the 20th century and the early effects of the "information explosion" began to be felt, the Serial Set became more limited in scope -- more specialized, with a focus on Congressional publications. Even so, it includes reports of investigations into Pearl Harbor, the Black Panthers, the Iran-Contra affair, and much, much more.
The LexisNexis U.S. Serial Set Digital Collection product is a mammoth project, under way for several years and expected to be complete by the end of 2005. A status report is available here. The database actually will include more than the post-1816 Serial Set, also incorporating the less well-organized documents, known as the American State Papers, of the first 14 Congresses (1789-1816). Coverage will extend forward to 1969.