Most laws start out as bills, which may be amended several times before finally being passed into law. (A law may also arise from a joint resolution, but this is much less common.) An analysis of these changes can shed light on what Congress ultimately hoped to achieve in enacting the law, although the reasoning behind the addition or deletion of a specific provision is not always readily apparent. Bills are also studied by researchers interested in failed or pending legislation. When examining bills as part of a legislative history, keep in mind that multiple bills are often introduced on the same topic, sometimes over the course of more than one session of Congress, even though only one of these bills is eventually passed into law. It is not unusual, for example, for the House of Representatives to pass a bill that is then "approved" by the Senate with the proviso that all of the language of the House bill after the enactment clause be struck and replaced with the wording of a similar Senate bill.
There are many different bill versions that arise during the legislative process from introduction through passage by both chambers:
Bills from 1989 to the present can be found in the following sources online. The University of California at Berkeley Library has created an online tutorial showing how to find recent bills in THOMAS.
Bills from 1981 to the present can be found in the D'Angelo Law Library Microfiche Collection. You should consult the Final Cumulative Finding Aid, House and Senate Bills to determine the fiche number. Please see the Law Library Circulation Desk for help.
Microfiche: D'Angelo Law Library, microfcK41.H6B5 (House) & microfcK41.S4B5 (Senate) (from 1981)