For purposes of legislative history research, committee reports are often the most important source for determining legislative intent.
Congressional committee reports in general, and conference reports in particular, are the most important source of legislative history. Reports are issued for almost every bill that becomes a law, and there is usually a report from each of the House and Senate committees that considered the legislation. A report will accompany the bill when it is sent to the full chamber for debate and voting.
Reports usually reprint the text of the bill, describe its purposes, and give reasons for the committee's recommendations on the bill. Often, committee reports include the legislative history of the bill, the purposes of the bill, and what the committee regards as the need for new legislation. There is often a "section-by-section" analysis of the bill that is very helpful if your research is concentrated on just one section or sections.
If a conference committee was appointed to draft a compromise bill acceptable to both the House and Senate (this occurs when the House and Senate versions of the bill are different), a conference report will be issued. Conference reports are particularly important because they come at the end of the legislative process and report on the text of the compromise bill. Conference committee reports are issued as House Reports (i.e. their citations will be H. Rpts.).