A United States congressional hearing is the principal formal method by which United States congressional committees collect and analyze information in the early stages of legislative policymaking. Whether confirmation hearings (a procedure unique to the United States Senate), legislative, oversight, investigative, or a combination of these, all hearings share common elements of preparation and conduct. Hearings usually include oral testimony from witnesses and questioning of the witnesses by members of Congress. George B. Galloway termed congressional hearings a goldmine of information for all the public problems of the United States. A leading authority on U.S. government publications has referred to the published hearings as "the most important publications originating within Congress." The Senate Library in a similar vein noted "Hearings are among the most important publications originating in Congress."
Hearings were not published generally until the latter part of the 19th century, except some early hearings (generally of special investigative committees) were published in the series that are part of the Serial Set. Published hearings did not become available for purchase from the United States Government Printing Office until 1924 and were not distributed to depository libraries until 1938. Unlike the documents and reports that are compiled in the Serial Set "hearings do not constitute a real series" although in the modern era a trend toward uniformity of numbering has resulted in all Senate hearings and prints for each Congressional Session (commencing with the 98th Congress in 1983) being assigned a unique numerical designation (in the style of what one scholar dubbed a "combination code") published on the cover and title page (e.g. S. HRG. 110-113; S. PRT. 110-13). A growing number of House Committees are assigning numerical or alphabetical designations for their publications (e.g. 110-35, 110-AA).
