The National Archives and Records Administration is the federal agency charged with preserving the federal records deemed to be of historic value. While their collections are vast (over 10 billion pages of text and millions of other items such as maps, photographs, film, sound recordings and electronic data), they in fact only preserve between 2 and 5 per cent of all the records generated by the federal government in any given year.
The National Archives were established in 1934 but hold records dating right back to 1775. As well as the main National Archives facilities, NARA runs a network of Federal Records Centers and Presidential Libraries for every president since Herbert Hoover.
NARA manages around 50 National Archives facilities in 17 states all throughout the US. These include archival reading rooms, federal records centers, Presidential libraries and various other affiliated institutions.
The major research locations for national records are Archives I in downtown Washington, DC, and Archives II in College Park, Maryland.
Archives I is the original facility, located on Pennsylvania Avenue between the White House and the Capitol (nearest Metro - Archives-Navy Memorial). It contains the Center for Legislative Archives and records dating from before 1945, as well as the tourist side of things, with exhibitions, an extensive visitor center, and the Rotunda with the Declaration of Independence, Constitution and Bill of Rights on permanent display.
Archives II was built in the early 1990s to relieve space pressures at Archives I and contains records dating from 1945-. It is located at 8601 Adelphi Road, College Park, Maryland. It can be reached by bus during the week; there is also a free shuttle bus for staff which leaves from Archives I and will take researchers too if there's space. On Saturdays the free shuttle runs for researchers.
Not all records are described in the online catalogues. The National Archives have made great progress in recent years with cataloguing and now estimate that 95% of their collections are catalogued at least to the series level, but the proportion and level of detail catalogued varies.
There are extensive printed finding aids and research staff on hand in the reading rooms to help you locate records when you arrive. You are strongly advised to contact the archives before visiting to find out what may be available and where.
You can register as a researcher and obtain a National Archives Research Card at any of their locations. You will need to show official ID, so bring your passport with you!
The National Archives have very strict regulations about what may be brought into their facilities, and full airport-style security checks are in place.
Most records in the National Archives are old enough (30+ years) that they are unrestricted and open for research (unless they are classified), but anything more recent from federal agencies may need to be requested under the Freedom of Information Act. This also applies to records in the Presidential Libraries which are subject to the Presidential Records Act (Reagan, George H.W. Bush, Clinton, George W. Bush). FOIA requests can take some time to process and will incur a fee. There is an extensive guide to how to make FOIA requests with the National Archives on their website.