When researching bills, committee hearings, and committee reports, you are performing legislative history research, essentially researching documents created at each stage of the legislative process as a bill is introduced and proceeds through steps of the formal legislative process.

Various versions of bills (produced as they move through the legislative process) can be researched. The first step of the legislative process is initiated when a bill is introduced into Congress.  After it is introduced and is assigned a bill number, and printed, it can be referred in and out of various committees. During this process, bill are often are amended and can be printed a number of times before their final passage. Comparing the various versions of a bill as it moves through the legislative process, including addition, deletion or modification of language in the versions of the bill, can be illuminative as to the intent of the drafters. 

Hearings are held by committees and sub-committees to obtain background information on pending legislation, and also for investigative purposes. Published hearings can include oral testimony, written statements of witnesses, exhibits, studies, article reprints, & texts of bills under consideration.

Committee reports can be especially useful sources of legislative history at the federal level, as they often include a bill's purpose and scope, a section-by section analysis, reasons for recommending full chamber approval, any views of dissenting committee members, as well as cost and budgeting information. Conference committee reports are a compromise of the House and Senate versions of a bill and indicate the understanding of both houses.