Hearings come in several varieties—legislative and oversight are most common—and any hearing can be published or unpublished. Not all congressional hearings are published, as each committee makes its own decision regarding which hearings are to be published. The transcripts of unpublished hearings are transferred to the National Archives. Senate hearings generally remain closed for 20 years, and House hearings remain closed for 30 years. Hearings that contain classified or sensitive material generally remain closed for 50 years. When they are released, unpublished hearings are not normally published by the committees, although in unusual circumstances they may be. ProQuest Congressional provides online access to published as well as some unpublished hearings. There is also an annotated print index by that same publisher for unpublished Senate and House hearings.
ProQuest Congressional Published Hearings (PDF): 1824 – date
HeinOnline: 1927 - 1994; contains Covington & Burling’s collection of Congressional Hearings
Proquest Legislative Insight: 1929 - forward (in progress) for legislation that became law.
CIS fiche set (UES in law library): 1970 – date
Print (title search in Orbis): various
Government Printing Office (PDF): 1995 - date
Lexis and Westlaw (unofficial transcripts): mid 1980s – date
Each committee decides which of its hearings are to be published. A committee may decide not to publish a hearing because it contains classified or sensitive information, because it pertains to private legislation, etc. The National Archives has the transcripts of unpublished hearings. Senate hearings generally remain closed for 20 years, and House hearings remain closed for 30 years. Hearings that contain classified or sensitive material generally remain closed for 50 years.
Yale's Mudd Library has the CIS unpublished hearings fiche set from 1789 to present. Yale also subscribes to ProQuest Congressional, which contains annotated indexing for unpublished hearings (Senate unpublished hearings from 1824-1984, and for House unpublished hearings from 1833-1972) and the full text of released hearings (1973 -1976).