The Public Law Number (Pub. L.) of an enacted statute is often the key to unlocking legislative history. It lets you know which Congress passed a law, and the law's place in the chronology of passed bills for that session.
The first public law to pass a Congress is designated number "1". Pub. L. No. 105-1 was the first bill enacted in the 105th Congress. Each subsequent public law is numbered sequentially throughout the two-year term of a Congress. As an example, the 105th Congress passed Public Law 105-264 in 1988, as its 264th enacted bill. Titled the "Travel and Transportation Reform Act of 1998," it requires federal employees to use federal charge cards when traveling.
When seeking information on legislative history, the public law number often acts as the most important descriptor of a particular law.
When you have a statutory citation, look at an annotated U.S. Code such as: U.S.C.A or U.S.C.S.
You are looking for the Source Credit or Source Note. It is at the end of the statutory language. It provides a list of all the laws that have created or affected the U.S. Code section at issue. For example, here is a Source Credit, from Westlaw, for 42 U.S.C.A. § 7604, which authorizes citizen suits to enforce air pollution emission standards.
Here you see the Public Law numbers (in blue), date of passage, and the Statutes at Large citation.
(Note: Statutes at Large are all laws and resolutions enacted during a session of Congress. The bound volume, Statutes at Large, is published after the session ends and arranged chronologically by Public Law). See Statutes At Large LAW FEDERAL 1st floor KF 50 .U545 (also available on HeinOnline and GovInfo)
For additional details, the Library of Congress has specific guidance on "How to Trace Federal Legislation."
If you know the name of an act,
If you need to find the bill number to use one of these compilations, and you know the public law number, you can find the bill number in the Statutes at Large. To obtain the bill numbers for early Congresses (1st to 57th, 1789 - 1903), consult: