Since 1957, each law enacted by Congress has been assigned a public law (P.L. or Pub. L.) number. Public law numbers are assigned in sequential order. The first part of the number designates the particular Congress that enacted the law and the second part designates the specific law enacted during that Congress (e.g., P.L. 104-35 refers to the 35th law passed during the 104th Congress).
If the piece of legislation you are interested in was enacted into law (thereby becoming a statute), the public law number will be of help to you in researching that law's legislative history. The United States Code can be used to identify the public law number (or numbers) for a particular statute. For guidance on how to find statutes in the United States Code, consult the USC Law Library guide Finding Federal Primary Law.
If you look up a statutory section in the code, you will typically see, immediately after the code section, a parenthetical note that provides the public law number for the act that created that section. And if your code section was subsequently amended, the note will also include the public law number for each act that amended your section.
It is important that you identify which public law introduced the particular statutory language in which you are interested. In the code, there will be statutory notes accompanying the code section to help you determine if the language you are interested in was contained in the original version of the code section or whether it was added in one of the subsequent amendments. Once you determine this, you can then select the appropriate public law number to use in your research.
Sometimes, you will be able to find a book or article that either brings together many of the relevant documents pertaining to a particular statute or at least provides citations to, and/or excerpts from, these documents. These types of sources are known as compiled legislative histories. Sources for compiled legislative histories include the following: