To find the legislative history of a law, you must first determine its public law number. For example, the Patriot Act was the 56th law enacted in the 107th Congress, and is also known as Public Law 107-56.
For ease of use, laws are grouped together by subject in a "code". If you know the name of a federal law, you can find its public law number by checking the Popular Name Table of the United States Code Annotated (Reference 2nd Floor KF 62 .W4).
A Congressional session lasts two years; each year is a session. If a bill does not become law by the end of the Congress in which it is introduced, it "dies". What Congress and session are we in now?
A legislative history* is the record of a law's passage through Congress, from its introduction as a bill to its final version as an act. It can shed light on a law's meaning and purpose, and on the reasons for its enactment. A legislative history usually contains the following primary source documents:
Useful, but not necessarily included, are:
For a detailed explanation of legislative history and how it is used, please see: Federal Legislative History Research: A Practitioner's Guide to Compiling the Documents and Sifting for Legislative Intent (Law Librarians' Society of Washington, DC)
*Note: this guide focuses on federal legislative history, but some state information is included on the next page, "Find a history."